Hand-book of physiology;

43
, Worn .

#0) bs beberaabidlh. ios ha atetabe

s = ;
§
4 a
: :

nie

/ =
:
- a
3
:
ae
n
*s* =

wtih

TW

yy

hy}
ae.

1

hig

a

i it ee ee

‘3

‘<7 4 “ie
eit,
OF “

3

a

~
*

"

~ i , “ PS) 4 ar
S ; ’ : GS “Se: |
\ a
\ 2 ‘ > -
e « . ¥ ¢ p \t>
: . . » ==
- ; ~

~ at
ee

: i
en SE Sai ert ME

HAND-BOOK

PHYSIOLOGY.

“ «Aetiga —_ —
FSi gce. |. ee a

oe

a a

HAND-BOOK

OF

PHYSIOLOGY.

BY WILLIAM SENHOUSE KIRKES, M.D.

EDITED BY

W. MORRANT BAKER, F.R.C.S.

LECTURER ON PHYSIOLOGY, AND
ASSISTANT SURGEON TO ST. BARTHOLOMEW’S HOSPITAL SURGEON TO THE
EVELINA HOSPITAL FOR SICK CHILDREN,

WITH TWO HUNDRED AND FORTY-EIGHT ILLUSTRATIONS.

WA

Gighth Gdition.
es A$

4 |

\9

LONDON:
JOHN MURRAY, ALBEMARLE STREET.
| 1872.

iy t ‘? f ore, .# ris Oy «OP. ; ' a
| - BRADBURY, AGNEW, & ©0., PRINTERS, ETA,
; ai Re ‘ : f

»
‘ > ~

at

PREFACE TO THE EIGHTH EDITION.

+

THE Eighth Edition is the result of an increased
‘demand for this work, involving the necessity for
a reprint at an earlier period after the publication of
the Seventh Edition than was anticipated, The oppor-
' tunity has been seized for making corrections and addi
tions where they appeared to be most needed ; but the ~
present issue must be regarded as, in great part, a

reprint of the Edition of 1869.

W. MORRANT BAKER.

THe CoLLEGE, St. BARTHOLOMEW’S HOSPITAL,
October, 1872.

ibe

Digitized by the te Archive
in, 2007 with func lime sai

CONTENTS.

peed Yaa

CHAPTER I.

THe GENERAL AND DISTINCTIVE CHARACTERS OF LIVING
BEINGS

CHAPTER II,

CHEMICAL COMPOSITION OF THE HumMAN Bopy

CHAPTER III.

StTrucTURAL COMPOSITION OF THE HumMAN Bopy

CHAPTER IV.

' STRUCTURE OF THE ELEMENTARY TISSUES. ; <
Epithelium . ‘ ‘ : ;
Areolar, Cellular, or Connective Tissue

Adipose Tissue
Pigment
Cartilage . ‘ .
Bones and Teeth : :
CHAPTER V.
Ture BLoop .

Quantity of Blood
Coagulation of the Blood

PAGE

19

Vili CONTENTS.

THE Boop, continued.
Conditions affecting Coagulation ‘ : ; ose 66
Chemical Composition of the Blood : ; : : 68
The Blood-Corpuscles, or Blood-Cells . yeas sree 69
Chemical Composition of Red Blood-Cells if 5 ‘ 74
Blood-Crystals . ; , ; , ‘ ; ote, ib.
The White Corpuscles . . poet, ae é 76

The Serum 78
Variations in the Prinekpal Constizhents of the Ticade
Sanguinis . 79

Variations in Healthy Blood reece Different Cirenmabatioes 83
Variations in the Composition of the Blood in Different

‘parts of the Body . ‘ : : : ; 5 ae 84.
Gases contained in the Blood . ; é : ‘ ¢ 89
Development of the Blood . ‘ ‘ ; ‘ Ya go
Uses of the Blood . ‘ ee 95:
Uses of the various Cenniitaunka of the Blood ; Bl ia ab...

CHAPTER VI.

CIRCULATION OF THE BLoop . ; > ae 99
_ The Systemic, Pulmonary, and Portal Gireulation ‘ ; 10B

THE Heart. ‘ ‘ ; *+? 102
Structure of the Valves of the Heart : ; 4 : 104
The Action of the Heart . > . ce < y 109
Function of the Valves of the Heart A eine > 4 112
Sounds of the Heart . ; ‘ : ‘ ; rh 119
Impulse of the Heart. . ‘ ‘ ; 122
Frequency and Force of the Heart’s heladh ; a: 124.
Cause of the Rhythmic Action of the Heart . , : 128
Effects of the Heart’s Action . : ; : pF ee 132

THE ARTERIES . ; : : : ; : 133
Structure of the ‘Arteries ; _ ; ‘ ‘ 5 and ib.
The Pulse : ; ; ; ; ‘ ‘ ‘ ‘ 143
Sphygmograph . : ; Sen ee 146
Force of the Blood in the Arteries : ° ‘ o Bhd 152
Velocity of the Blood inthe Arteries. . . oie 155

CONTENTS. 1X

PAGE

Tue CAPILLARIES . é ‘ F 155
The Structure and Avvehaesaurt of Capillaries: , PSR 156
Circulation in the Capillaries . ‘ : ‘ ‘ ‘ 160.

THE VEINS : , : ‘ P ; ; . rth 167

Structure : . ‘ . ab.
Agents concerned in ith Oireulation of the Blood ae 173
Velocity of Blood in the Veins ; ; : ; ‘ 175
Velocity of the Circulation ; ‘ - , c's 176

PECULIARITIES OF THE CIRCULATION IN DIFFERENT PARTS 180.
Cerebral Circulation ‘ 2 - 4 az : ‘ tb.
Erectile Structures. , ; é ? - winx 183,

CHAPTER VIE.

RESPIRATION , ; : ; ; ; 186
Position and Str pethare of the tain ‘ j : tee ib.
Mechanism of Respiration i é . 5 , ‘ 194.
Respiratory Movements . ; < : i wy 195
Respiratory Khythm : . ‘ . : ; 200
Respiratory Movements of Glottis 3 ‘ b Way tb.
Quantity of Air respired ‘ : ’ 205
Movements of the Blood in eenieatary Organs 4 aig 208
Changes of the Air in Respiration . : d 210
Changes produced in the Blood by Waspination’ i ims 219
Mechanism of various Respiratory Actions .- . ; 220
Influence of the Nervous System in Respiration . gts 225
Effects of the Suspension and Arrest of Respiration . ‘ 227

CHAPTER VIII.

ANIMAL HEAT , : ‘ : : . Pid 231
Variations in Penbiainde ‘ , 232
Sources and Mode of Production of Heat in the Rody ‘ 236
Regulation of Temperature. ana ‘ ‘ ‘ 238
Influence of Nervous System. ; . ‘ aT 243

,

x i CONTENTS.

CHAPTER IX.

DIGESTION . : 4 .: . : : ’
Food *
Starvation

PASSAGE OF FoopD THROUGH THE ALIMENTARY CANAL
The Salivary Glands and the Saliva
Passage of Food into the Stomach

DIGESTION OF Foop IN THE STOMACH .
Structure of the Stomach ‘
Secretion and Properties of the Gabtrie Fluid .
Changes of the Food in the Stomach .
Movements of the Stomach :
Influence of the Nervous System on Cesise Digestion
Digestion of the Stomach after Death

DIGESTION IN THE INTESTINES ;
Structure and Secretion of the Small Intestines
Valvule Conniventes . ;
Glands of the Small Intestine P
The Villi .
Structure of the Laie Iotmutine-
The Pancreas and its Secretion .
Structure of the Liver
Functions of the Liver
The Bile :
Glycogenic Function of the Liver
Summary of the Changes which take inte in the Food
during its Passage through the small Intestine
Summary of the Process of Digestion in the large Intestine
Gases contained in the Stomach and Intestines
Movements of the Intestines .

CHAPTER X.

ABSORPTION
Structure and Office of the Leste and Uymphatic Vessel
and Glands . . . 3 : ,
Lymphatic Glands

354

CONTENTS.

ABSORPTION, continued.
Properties of Lymph and Chyle
Absorption by the Lacteal Vessels
Absorption by the Lymphatics
Absorption by Blood- Vessels

CHAPTER XI.
NvuTRITION AND GROWTH
NUTRITION
GROWTH
CHAPTER XII.
SECRETION

SECRETING MEMBRANES
Srrovus MEMBRANES .
Mucous MEMBRANES
SECRETING GLANDS
PROCESS OF SECRETION .

CHAPTER XIII.

VASCULAR GLANDS; OR GLANDS WITHOUT DucTs .

Structure of the Spleen
Functions of the Vascular Glands

CHAPTER XIV.

Tuer SKIN AND ITs SECRETIONS
Structure of the Skin
Structure of Hair and Nails
Excretion by the Skin
Absorption by the Skin .

394
395
396
398
401

404,

410
4il
414

419

ab.
428
432
437

xii CONTENTS.

CHAPTER XV.

Tue KIDNEYS AND THEIR SECRETION . ‘ : .
Structure of the Kidneys
Secretion of Urine ;
The Urine ; its general Brovextion : : ‘ . ‘
Chemical Composition ofthe Urine .° . - gy

CHAPTER XVI.

Tue Nervous SystEM ;
Elementary Structures of the N ervous ‘ayatom
Functions of Nerve-Fibres
Functions of Nerve-Centres

CEREBRO-SPINAL NERVOUS SysTEM. : ;
Spinal Cord and its Nerves . ‘ : : é
Functions of the Spinal Cord

THE MEDULLA OBLONGATA . ;
Its Structure 4
Distribution of the Fibres of the Medulla Oblonaaia
Functions of the Medulla Oblongata . , ‘ ‘

STRUCTURE AND PuHysIOLOGy OF THE Pons VAROLII, CRURA
CEREBRI, CORPORA QUADRIGEMINA, CorroRA GENICU-
LATA, Optic THALAMI, and Corpora STRIATA .

Pons Varolii

Crura Cerebri

Corpora Quadrigemina
The Sensory Ganglia

STRUCTURE AND PHYSIOLOGY OF THE CEREBELLUM

STRUCTURE AND PHYSIOLOGY OF THE CEREBRUM

PHYSIOLOGY OF THE CEREBRAL AND SPprnAL NERVES ‘
Physiology of the Third, Fourth, and Sixth Cerebral or
Cranial Nerves . A ‘
Physiology of the Fifth or Trigeratoel Werve
Physiology of the Facial Nerve . ‘

PAGE
440
ab.
446
448
450

463
464
474.
483

488
tb.
495

509

tb.
511
513.

CONTENTS. Xill

PAGE

PHYSIOLOGY OF THE CEREBRAL AND SPINAL NERVES, continued.
Physiology of the Glosso-Pharyngeal Nerve. ; : 553
Physiology of the Pneumogastric Nerve . : are 557
Physiology of the Spinal Accessory Nerve ; : . 564
Physiology of the Hypoglossal Nerve . . : sofa 565
Physiology of the Spinal Nerves. ‘ : ; : 567

-PHYSIOLOGY OF THE SYMPATHETIC NERVE . r i ab,

CHAPTER XVII.

CAUSES AND PHENOMENA OF MOTION . F ; ; ; 578
Cin1ARY Morion . ; : ; ; ; ae ab.
Muscutar Motion » | RE. 5 a 309; BBO
Muscular Tissue : , ‘ p . 5 grees ab.
Properties of Muscular issue : . : ; ‘ 587
Action of the Voluntary Muscles : ‘ ‘ ae 595
Action_of the Involuntary Muscles ? ‘ : ‘ 602
Source of Muscular Action j i : : ave g tb.

CHAPTER XVIII.

Or Voice AND SprEcH ; : ; : 604
Mode of Production of the Bunn Veioe . . Se ib.
The Larynx . ‘ ‘ : 606
papeeatian of the Vanes in Shaving: and Sealkine eid 614

Risin , . ‘ ; ; ; ; - ; ; 619

CHAPTER XIX.

THE SENSES . ‘ ; ; ; : ; 7% 622

» Tue SENSE OF ices: : ; - ; ; ‘ ; 630
Tue SENSE OF SIGHT ‘ ays : 4 ‘wr 636

Structure of the Eye . ‘ , d ‘ ‘ ‘ ib.
Phenomena of Vision . dey 645

Reciprocal Action of different Sachs of the Rating ‘ 661
Simultaneous Action of the two Eyes . : sist 664.

Xiv

CONTENTS.

THE SENSE OF HEARING

Anatomy of the Organ of Biatng

Physiology of Hearing

Functions of the External Ear:

Functions of the Middle Ear ; the Tympanum, Ossicul
and Fenestre :

Functions of the Internal Ear

Sensibility of the Auditory Nerve

THE SENSE OF TASTE. : Z ‘ : i

THE SENSE oF TovucH

CHAPTER XX.

GENERATION AND DEVELOPMENT

Generative Organs of the Female
Unimpregnated Ovum
Discharge of the Ovum

Corpus Luteum .

IMPREGNATION OF THE OvuM

Male Sexual Functions

DEVELOPMENT

Changes of the Ovum sieevioits to the oemation of the
Embryo . ‘ : ‘ af As

Changes of the Ovum withi the icra ‘ ; ,

The Umbilical Vesicle

The Amnion and Allantois

The Chorion

Changes of the Macsils $etitenns of the Tierne aud
Formation of the Placenta

DEVELOPMENT OF ORGANS

Development of the Vertebral Calan and Cisalnna:
Development of the Face and Visceral Arches ©
Development of the Extremities

713
714
718
723
727

73%
40.

739

ad.
742
745
747
75%

752

758

.

760
762

SE

.
= er, hee Se

> Se a

a —

CONTENTS.

DEVELOPMENT OF ORGANS, continued. °
Development of the Vascular System
Circulation of Blood in the Foetus
Development of the Nervous System
Development of the Organs of Sense
Development of the Alimentary Canal
Development of the Respiratory Apparatus
The Wolffian Bodies, Urinary Apparatus, and Sexual Org gans

THE MAMMARY GLANDS .
INDEX

List OF WORKS REFERRED TO

re v A arin) ‘

rari. we
, ‘a is } oe
ot SY i‘ ts
~ ; :

aoe & ’ Fy bay o

4204
Qa oF

Dali of
ie]
we

+ orn ay a
co ae ae

;

HANDBOOK OF PHYSIOLOGY.

CHAPTER I.

ON THE GENERAL AND DISTINCTIVE CHARACTERS OF
LIVING BEINGS.

Human Puystotoey is the science which treats of the
life of man—of the way in which he lives, and moves, and
has his being. It teaches how man is begotten and born;
how he attains maturity ; and how he dies.

Having, then, man as the object of its study, it is un-
necessary to speak here of the laws of life in general, and
the means by which they are carried out, further than is
requisite for the more clear understanding of those of the
life of man if particular. Yet it would be impossible to
understand rightly the working of a complex machine
without some knowledge of its motive power in the sim-
plest form; and it may be well to see first what are the
so-called essentials of life—those, namely, which are mani-
fested by all living beings alike, by the lowest vegetable
and the highest animal, before proceeding to the consider-
ation of, the structure and endowments of the organs and
tissues belonging to man.

The essentials of life are these,—birth, growth and
development, decline and death—and an idea of what life
is, will be best gained by sketching these events, each in
succession, and their relations one to another.

The term, birth, when employed in this general sense
of one of the conditions essential to life, without reference

a f Bo

2 GROWTH.

to any particular kind of living being, may be taken to
mean, separation from a parent, with a greater or less
power of independent existence as a living being.

Taken thus, the term, although not defining any par-
ticular stage in development, serves well enough for the
expression of the fact, to which no exception has yet been
proved to exist, that the capacity for life in all living beings
is got by inheritance.

Growth, or inherent power of increasing in size, although
essential to our idea of life, is not a property of living
beings only. A crystal of sugar or of common salt, or of
any other substance, if placed under appropriate conditions
for obtaining fresh material, will grow in a fashion as
definitely characteristic and as easily to be foretold as that
of a living creature. It is, therefore, necessary to explain
the distinctions which exist in this respect between living
and lifeless structures; for the manner of growth in the
two cases is widely different.

First, the growth of a crystal, to use the same example
as before, takes place merely by additions to its outside;
the new matter is laid on particle by particle, and layer by
layer, and, when once laid on, it remains unchanged. The
growth is here said to be superjicial. In a living structure,
on the other hand, as, for example, a brain or a muscle,
where growth occurs, it is by addition of new matter, not
to the surface only, but throughout every part of the mass;
the growth is not superficial, but interstitial. In the second
place, all living structures are subject to constant decay ;
and life consists, not as once supposed, in the power of pre-
venting this never-ceasing decay, but rather in making up
for the loss attendant on it by never-ceasing repair. Thus,
a man’s body is not composed of exactly the same particles
day after day, although to all intents he remains the same
individual, Almost every part is changed by degrees; but
the change ‘is so gradual, and the renewal of that which is
lost.so exact, that no difference may be noticed, except at

DEVELOPMENT. | 3

long intervals of time. A lifeless structure, as a crystal,
is subject to no such laws; neither decay nor repair is a
necessary condition of its existence. That which is true of
‘structures which never had to do with life is true also with
respect to those which, though they are formed by living
parts, are not themselves alive. Thus, an oyster shell is
formed by the living animal which it encloses, but it is as
lifeless as any other mass of saline matter; and in accord-
ance with this circumstance its growth takes place not in-
terstitially, but layer by layer, and it is not subject to the
constant decay and reconstruction which belong to the
living. ‘The hair and nails are examples of the same
fact.

' Thirdly. In connection with the growth of lifeless
masses there is no alteration in composition or properties
of the material which is taken up and added to the pre-
viously existing mass. For example, when a crystal of
common salt grows on being placed in a fluid which con-
tains the same material, the properties of the salt are not
changed by being taken out of the liquid by the crystal
and added to its surface in a solid form. But the case is
essentially different from this in living beings, both animal
and vegetable. A plant, like a crystal, can only grow when
fresh material is presented to it; and this is absorbed by
its leaves and roots; and animals for the same purpose of
getting new matter for growth and nutrition, take food into
their stomachs. But in both these cases the materials are
much altered before they are finally assimilated by the
structures they are destined to nourish.
* Fourthly. The growth of all living things has a definite
limit, and the law which governs this limitation of increase
in size is so invariable that we should be as much astonished
to find an individual plant or animal without: limit as to
growth as without limit to life.

Development is as constant an accompaniment of life as

growth. The term is used to indicate that change to
: "Bz

4 ANIMALS CONTRASTED

which, before maturity, all living parts are constantly sub-
ject, and by which they are made more and more capable
of performing their several functions. For example, a
full-grown man is not simply a magnified child; his tissues
and organs have not only grown, or increased in size, they
have also developed, or become better in quality.

No very accurate limit can be drawn between the end of
development and the beginning of decline; and the two
processes may be often seen together in the same individual.
But after a time all parts alike share in the tendency to
degeneration, and this is at length succeeded by death.

The decline of living beings is as definite in its occur-
rence as growth or development. Death—not by disease
or injury—so far from being a violent interruption of the
course of life, is but the fulfilment of a purpose in view
from the commencement.

It has been already said that the essential features of
life are the same in all living things; in other words, in the
members of both the animal and vegetable kingdoms. It
may be well now to notice briefly the distinctions which
exist between the members of these two kingdoms. ~ It
wnay seem, indeed, a strange notion’that it is possible to
confound vegetables with animals, but it is true with
respect to the lowest of them, in which but little is mani-
fested beyond the essentials of life, which are the same in
both.

I. Perhaps the most essential distinction is the presence
or absence of power to live upon inorganic material; in
other words, to act chemically on carbonic acid, ammonia
and water, so as to make use of their cumponent elements
as food. Indeed one ought probably to say that a question
concerning the capability of the lower kinds of animal to
live in this way cannot be entertained; and that such
a manner of life should decide at once in favour of a
vegetable nature, whatever might be the attributes which
seemed to point to an opposite conclusion. The power of

WITH VEGETABLES. 5

living upon organic matter would: seem to be less decisive
of an animal nature, for some fungi appear to derive
support almost entirely from this source.

II. There is, commonly, a marked difference in general
chemical composition between vegetables and animals,
even in their lowest forms; for while the former consist
mainly of a substance containing carbon, hydrogen, and
oxygen only, arranged so as to form a compound closely
allied to starch, and called cellulose, the latter are com-
monly composed in great part of the three elements
just named, together with a fourth, nitrogen; the proxi-
mate principles formed from these being identical, or
nearly so, with albumen. It must not be supposed, how-
ever, that either of these typical compounds alone, with
its allies, is confined to one kingdom of nature. Nitro-
genous or albuminous compounds are freely produced
by vegetable structures, although they form an infinitely
smaller proportion of the whole organism than cellulose or
starch. And while the presence of the latter in animals
is much more rare than is that of the former in vegetables,
there are many znimals in which traces of it may be dis-
covered, and some, the Ascidians, in which it is found in
considerable quantity.

III. Inherent power of movement is a quality which we
so commonly consider an essential indication of animal
nature, that it is difficult at first to conceive it existing in
any other. The capability of simple motion is now known,
however, to exist in so many vegetable forms, that it can
no longer be held as an essential distinction between them
and animals, and ceases to be a mark by which the one
can be distinguished from the other. Thus the zoospores
of many of the Cryptogamia exhibit movements of a like
kind to those seen in animalcules; and even among the
higher orders of plants, many exhibit such motion, either
at regular times, or on the application of external irrita-
tion, as might lead one, were this fact taken by itself, to

6 ANIMALS CONTRASTED

regard them as sentient beings. Inherent power of move-
ment, then, although especially characteristic of animal
nature, is, when taken by itself, no proof of it. Of
course, if the movement were such as to indicate any kind
of purpose, whether of getting food or any other, the case
would be different, and we should justly call a being ex-
hibiting such motion, an animal. But low down in the
scale of life, where alone there exists any difficulty in
distinguishing the two classes, movements, although almost
always more lively, are scarcely or not at all more pur-
posive in one than the other; and even if we decide on the
animal nature of a being, it by no means follows that we
are bound to acknowledge the presence of sensation or
volition in the slightest degree. There may be at least
no evidence of its possessing a trace of those tissues,
nervous and muscular, by which, in the higher members
of the animal kingdom, these qualities are manifested.
Probably there is no more of either of them in the lowest
animals than in vegetables. In both, movement is effected
by the same means—ciliary action, and hence the greater
value, for purposes of classification, of the power to live
on this or that kind of food,—on organic or inorganic
matter. As the main purpose of the lowest members of
the vegetable kingdom is doubtless to bring to organic
shape the elements of the inorganic world around, so the
function of the lowest animal is, in like manner, to act on
degenerating organic matter,—‘“to arrest the fugitive
organized particles, and turn them back into the ascending
stream of animal life.” And, because sensation and voli-
tion are accompaniments of life in somewhat higher animal
forms, it is needless to suppose that these qualities exist
under circumstances in which, as we may believe, they
could be of no service. It is as needless as to dogmatise —
on the opposite side, and say that no feeling or voluntary
movement is possible without the presence of those tissues
which we call nervous and muscular.

WITH VEGETABLES. 7

IV. The presence of a stomach is a very general mark

by which an animal can be distinguished from a vegetable.

But the lowest animals are’ surrounded by material that
they can take as food, as a plant is surrounded by an
atmosphere that it can usein like manner. And every part
of their body being adapted to absorb and digest, they
have no need of a special receptacle for nutrient matter,
and accordingly have no stomach. ‘This distinction, then,
is not a cardinal one. |

It would be tedious as well as unnecessary to enumerate

‘the chief distinctions between the more highly developed

animals and vegetables. They are sufficiently apparent.
It is necessary to compare, side by side, the lowest mem-
bers of the two kingdoms, in order to understand rightly
how faint are the boundaries between them.

CHAPTER II.

.

CHEMICAL COMPOSITION OF THE HUMAN BODY.

Tue following Elementary Substances may be obtained by
chemical analysis from the human body: Oxygen, Hydro-
gen, Nitrogen, Carbon, Sulphur, Phosphorus, Silicon,
Chlorine, Fluorine, Potassium, Sodium, Calcium, Magne-
sium, Iron, and, probably as accidental constituents, Man-
ganesium, Aluminium, Copper, and Lead. Thus, of the
sixty-three or more elements of which all known matter is
composed, more than one-fourth are present in the human
body. F

Only one or two elements, and in very minute amount,
are present in the body uncombined with others; and
even these are present much more abundantly in various
states of combination. The most simple compounds formed

8 CHEMICAL COMPOSITION OF HUMAN BODY.

by union in various proportions of these elements are
termed prowimate principles; while the latter are classified
as the organic and the inorganic proximate principles.

The term organic was once applied exclusively to those
substances which were thought to be beyond the compass
of synthetical chemistry and to be formed only by or-
ganized or living beings, animal or vegetable; these
being called organized, inasmuch as they are charac-
terized by the possession of different parts called organs.
But with advancing knowledge, both distinctions have dis-
appeared; and while the title of living organism is applied
to numbers of living things, having no trace of organs in
the old sense of the term, and in some, so far as can be
now seen, in no other sense, the term organic has long
ceased to be applied to substances formed only by living
tissues. In other words, substances, once thought to be
formed only. by living tissues, are still termed organic,
although they can be now made in the laboratory. The
term, indeed, in its old meaning, becomes year by year
applicable to fewer substances, as the chemist adds to his
conquests over inorganic elements and compounds, and
moulds them to more complex forms.

Although a large number of so-called organic com-
pounds have long ceased to be peculiar in being formed
only by living tissues, the terms organic and inorganic are ~
still commonly used to denote distinct classes of chemical
substances, and the classification of the matters of which
the human body is composed into the organic and the
inorganic is-convenient, and will be here employed.

No very accurate line of separation can be drawn
between organic and inorganic substances, but there are
certain peculiarities belonging to the former which siny
be: here briefly noted.

I. Organic compounds are composed of a larger number
of Elements than are present in the more common kinds of
inorganic matter. Thus, albumen, fibrin, and gelatin, the

CHEMICAL COMPOSITION OF HUMAN BODY. 9

most abundant substances of this class, in the more highly
organized tissues of animals, are composed of five elements,
—carbon, hydrogen, oxygen, nitrogen, and sulphur. The
most abundant inorganic substance, water, has but two
elements, hydrogen and oxygen.

2. Not only are a large number of elements usually
combined in an organic compound, but a large number of
equivalents or atoms of each of the elements are united to
form an equivalent or atom of the compound. In the case
of carbonate of ammonium, as an example among inorganic
substances, one equivalent of carbonic acid is united with
two of ammonium; the equivalent or atom of carbonic acid
consists of one of carbon with two of oxygen; and that of
ammonium of one of nitrogen with three of hydrogen. But
in an equivalent or atom of fibrin, or of albumen, there
are of the same elements, respectively, 72, 22, 18, and
112 equivalents. . And together with this union of large
numbers of equivalents in the organic compound, it is
further observable, that the several numbers stand in no
simple arithmetical relation one with another, as the
numbers of equivalents combining in an inorganic com-
pound do.

With these peculiarities in the chemical composition of
organic bodies we may connect two other consequent facts;
first, the large number of different compounds that. are
formed out of comparatively few elements; secondly, their
great proneness to decomposition. For it is a general
rule, that the greater the number of equivalents or atoms
of an element that enter into the formation of an atom of
a compound, the less is the stability of that compound.
Thus, for example, among the various oxides of lead and
other metals, the least stable in composition are those in
which each equivalent has the largest number of equiva-
_lents of oxygen. So, water, composed of one equivalent
of oxygen and two of hydrogen, is not changed by any
slight force; but peroxide of hydrogen, which has two

Io CHEMICAL COMPOSITION OF HUMAN BODY,

equivalents of oxygen to two of hydrogen, is among the
substances most easily decomposed.

The instability, on this ground, belonging to organic
compounds, is, in those which are most abundant in the
highly organized tissues of animals, augmented, Ist, by
their containing nitrogen, which, among all the elements,
may be called the least decided in its affinities, and that
which maintains with least tenacity its combinations with
other elements; and, 2ndly, by the quantity of water
which, in their natural state, is combined with them, and
the presence of which furnishes a most favourable con-
dition for the decomposition of nitrogenous compounds.
Such, indeed, is the instability of animal compounds,
arising from these several peculiarities in their constitu-
tion, that, in dead and moist animal matter, no more is
requisite for the occurrence of decomposition than the
presence of atmospheric air and a moderate temperature; —
conditions go commonly present, that the decomposition of
dead animal bodies appears to be, and is generally called,
spontaneous. The modes of such decomposition vary ac-
cording to the nature of the original compound, the tem-
perature, the excess of oxygen, the presence of microscopic
organisms, and other circumstances, and constitute the
several processes of decay and putrefaction ; in the results
of which processes the only general rule seems to be, that
the several elements of the original compound finally unite
to form those substances, whose composition is, under the
circumstances, most stable. |

The organic compounds existing in the human body may
be arranged in two classes, namely, the azotized or nitro-
genous, and the non-azotized, or non-nitrogenous principles,

The non-azotized principles include the several fatty, oily,
or oleaginous substances, as olein, stearin, cholesterin, and
others. In the same category of non-nitrogenous substances
may be included lactic and formic acids, animal glucose,
sugar of milk, &e.

GELATINOUS SUBSTANCES. II

The oily or fatty matter which, enclosed in minute cells,
forms the essential part of the adipose or fatty tissue of the
human body (p. 38), and which is mingled in minute par-
ticles in many other tissues and fluids, consists of a mixture
of stearin, palmitin, and olein. The mixture forms a clear
yellow oil, of which different specimens congeal at from
45° to 35°.

Cholesterin, a fatty matter which melts at 293° F., and is
therefore, always solid at the natural temperature of the
body, may be obtained in small quantity from blood, bile,
and nervous matter. It occurs abundantly in many biliary
calculi; the pure white crystalline specimens of these con-
cretions being formed of it almost exclusively.. Minute
rhomboidal scale-like crystals of it are also often found
in morbid secretions, as in cysts, the puriform matter of
softening and ulcerating tumours, &c. It is soluble in
ether and boiling alcohol; but alkalies do not change
it; it is one of those -fatty substances which are not
saponifiable.

The azotized or nitrogenous principles in the human body
include what may be called the proper gelatinous and albu-
ninous substances, besides others of less definite rank and
composition, as pepsin and ptyalin, horny matter or keratin,
many colouring and extractive matters, &c.

The gelatinous substances are contained in several of the
tissues, especially those which serve a »passive mechanical
office in the economy; as the cellular, or fibro-cellular
tissue in all parts of the body, the tendons, ligaments,
and other fibrous tissues, the cartilages and bones, the
skin and serous membranes. These, when boiled in
water, yield a material, the solution of which remains
liquid while it is hot, but becomes solid and jelly-like on
cooling.

Two varieties of these substances are described, gelatin
and chondrin, the latter being derived from cartilages,
the former from all the other tissues enumerated above,

12 CHEMICAL COMPOSITION OF HUMAN.BODY.

and in its purest state, from isinglass, which is the swim-
ming bladder of the sturgeon, and which, with the excep-
tion of about 7 per cent. of its weight, is wholly reducible
into gelatin. The most characteristic property of gelatin
is that already mentioned, of its solution being liquid when
warm, and solidifying or setting when it cools. The tem-
perature at which it becomes solid, the proportion of gela-
tin which must be in solution, and the firmness of the
jelly when formed, are various, according to the source,
the quantity, and the quality of the gelatin; but, as a
general rule, one part of dry gelatin dissolved in 100 of
water, will become solid when cooled to 60°. The solidi-
fied jelly may be again made liquid by heating it, and the
transitions from the solid to the liquid state by the alter-
nate abstraction and addition of heat, may be repeated
several times ; ,but at length the gelatin is so far altered,
and, apparently, oxydized by the process, that it no longer
becomes solid on cooling. Gelatin in solutions too weak
to solidify when cold, is distinguished by being precipitable
with alcohol, ether, tannic acid, and bichloride of mercury,
and not precipitable with the ferrocyanide of potassium.
The most delicate and striking of these tests is the tannic
acid, which is conveniently supplied in an infusion of oak-
bark or gall-nuts; it will detect one part of gelatin in
5,000 of water; and if the solution of gelatin be strong
it forms a singularly dense and heavy precipitate, which
has been named tanno-gelatin, and is completely insoluble
in water.

Chondrin, the kind of gelatin obtained from cartilages,
agrees with gelatin in most of its characters, but its
solution solidifies on cooling much less firmly, and, unlike
gelatin, it is precipitable with acetic and the mineral and
other acids, and with alum, persulphate of iron and acetate
of lead.

Albuminous substances, or proteids, as they are sometimes
called, exist abundantly in the human body. The chief

ALBUMEN. 13

among them are albumen, fibrin, casein, syntonin, myosin,
and globulin.

tbumen exists in most of the-tissues of the body, but
especially in the nervous, in the lymph, chyle, and blood,
and in many morbid fluids, as the serous secretions of
_dropsy, pus, and others. In the human body it is most
abundant, and most nearly pure, in the serum of the blood.
In all the forms in which it naturally occurs, it is com-
bined with about six per cent. of fatty matter, phosphate
of lime, chloride of sodium, and other saline substances.
Its most- characteristic property is, that both in solution
and in the half-solid state in which it exists in white-of-
egg, it is coagulated by heat, and.in thus becoming solid,
becomes insoluble in water. ‘The temperature required
for the coagulation of albumen is the higher the less
the proportion of albumen in the solution submitted
to heat. Serum and such strong solutions will begin to
coagulate at from 150°.to 170°, and these, when the
cheat is maintained, become almost solid and opaque.
But weak solutions require a much higher temperature,
even that of, boiling, for their coagulation, and either only
become milky or opaline, or produced flocculi which are
precipitated.

Albumen, in the state in which it naturally occurs, ap-
pears to be but little soluble in pure water, but is soluble
in water containing a small proportion of alkali. In such
solutions it is probably combined chemically with the
alkali; it is precipitated from them by alcohol, nitric, and
other mineral acids, by ferrocyanide of potassium (if before
or after adding it the alkali combined with the albumen be
neutralised), by bichloride of mercury, acetate of lead, and
most metallic salts.

Coagulated albumen, i.c., albumen made solid with heat,
is soluble in solutions of caustic alkali, and in acetic acid
if it be long digested or boiled with it. With the.aid of
heat, also, strong hydrochloric acid dissolves albumen pre-.

a

*

14 CHEMICAL COMPOSITION OF HUMAN BODY.

viously coagulated, and the solution ‘has a beautiful purple
or blue colour.

Fibrin is found most abundantly in the blood and the
more perfect portions of the lymph and chyle. It is very
doubtful, however, whether fibrin, as such, exists in these
fluids,—whether, that is to say, it is not itself formed at
the moment of coagulation. (See Chapter on the Blood.)

Tf a common clot of blood be pressed in fine linen while
a stream of water flows upon it, the whole of the blood-
colour is gradually removed, and strings and various pieces |
remain of a soft, yet tough, elastic, and opaque-white sub-_
stance, which consist of fibrin, impure, with a mixture of
fatty matter, lymph-corpuscles, shreds of the membranes
of red blood-corpuscles, and some saline substances. Fibrin
somewhat purer than this may be obtained by stirring blood
while it coagulates, and collecting the shreds that attach
themselves to the instrument, or by retarding the coagula-
tion, and, while the red blood-corpuscles sink, collecting
the fibrin unmixed with them. But in neither of these
cases is the fibrin perfectly pure.

Chemically, fibrin and albumen can scarcely be distin-
guished ; the only difference apparently being that fibrin
contains 1°5 more oxygen in every 100 parts than albumen
does. Mr. A. H. Smee has, indeed, apparently converted
albumen into fibrin, by exposing a solution to the prolonged
influence of oxygen. Nearly all the changes, produced by
various agents, in coagulated albumen, may be repeated
with coagulated fibrin, with no greater differences of result
than may be reasonably ascribed to the differences in the
mechanical properties of the two substances. Of such dif-
ferences, the principal are, that fibrin immersed in acetic
acid swells up and becomes transparent like gelatin, while
albumen undergoes no such apparent change; and that
deutoxyde of hydrogen is decomposed when in contact with
coagulated fibrin, but not with albumen.

Casein, which is said to be albumen in combination with

SYNTONIN: MYOSIN. 15

soda, exists largely in milk, and forms one of its most im-
portant constituents.

Syntonin is obtained from muscular tissue, both of the
striated and organic kind. It differs from ordinary fibrin
in several particulars, especially in being less soluble in
nitrate and carbonate of potash, and more soluble in dilute
hydrochloric acid.

Myosin is the substance which spontaneously Seagulates
in the juice of muscle. It is closely allied to syntonin ;
indeed, in the act of solution in eee acid, it is converted
into it.”

The per-centage composition of albumen, fibrin, gelatin,
and chondrin, is thus given by Mulder:—

Albumen. Fibrin. Gelatin. | Chondrin.

Carbon. 53°5 52°7 50°40 49°97
Hydrogen 7°O 69 6°64 6°63
Nitrogen : 15°5 15"4 18°34 14°44
Oxygen... 22'0 235. Ib aang | tL 28°58
Sulphur ae 1°6 12 |f 74 f 0°38
Phosphorus . : 0"4. 0°3

| 100°0 100°0 100'00 100'00

Horny Matter.—The substance of the horny tissues, in-
cluding the hair and nails (with whale-bone, hoofs, and
horns), consists of an albuminous substance, with larger
proportions of sulphur than albumen and fibrin contain.
Hair contains 10 per cent. and nails 6 to 8 per cent. of
sulphur.

The horny substances, to which Simon applied the name
of keratin, are insoluble in water, alcohol, or ether; soluble
in caustic alkalies, and sulphuric, nitric, and hydrochloric
acids; and not precipitable from the solution in acids by
ferrocyanide of potassium.

Mucus, in some of its forms, is related to these horny

~ substances, consisting, in great part, of epithelium detached

16 CHEMICAL COMPOSITION OF HUMAN BODY. .

from the surface of mucous membrane, and floating in a
peculiar clear and viscid fluid. But under the name of
mucus, several various substances are included of which
some are morbid albuminous secretions containing mucus
and pus-corpuscles, and others consist of the fluid secretion
variously altered, concentrated, or diluted. Mucus contains
an albuminous substance, termed mucin. It differs from
albumen chiefly in not containing sulphur.

Pepsin and other albuminous ferments, as they are some-
times called, will be described in connection with the secre-
tions of which they are the active principles. And the
various colouring matters, as of the blood, bile, &c., will be
also considered with the fluids or tissues to which they
belong.

Besides the above-mentioned organic nitrogenous com-
pounds, other substances are formed in the living body,
chiefly by decomposition of nitrogenous materials of the
food and of the tissues, which must be reckoned rather as
temporary constituents than essential component parts of
the body; although from the continual change, which is a
necessary condition of life, they are always to be found in
greater or less amount. Examples of these are urea, uric,
and hippuric acid, creatin, creatinin, leucin, and many
others.

_ Such are the chief organic substances of which the
human body is composed. It must not be supposed, how-
ever, that they exist naturally in a state approaching that
of chemical purity. All the fluids and tissues of the body
appear to consist, chemically speaking, of mixtures of
several of these principles, together with saline matters:
Thus, for example, a piece of muscular flesh would yield
fibrin, albumen, gelatin, fatty matters, salts of soda,
potash, lime, magnesia, iron, and other substances, such as
creatin, which appear passing from the organic towards
the inorganic state. This mixture of substances may be
explained in some measure by the existence of many

WATER: POTASH’; SODA. ~~. 17

different structures or tissues in the muscles; the gelatin
may be referred principally to the cellular tissue between
the fibres, the fatty matter to the adipose tissue in the
same position, and part of the albumen to the blood and
the fluid by which the tissue is kept moist. But, beyond
these general statements, little can be said of the mode in
which the chemical compounds are united to form an
organized structure; or of how, in any organic body, the
several incidental substances are combined with. those
which are essential.

The inorganic matters which exist as such in the human
body are numerous.

Water forms a large proportion, probably more than

two-thirds of the weight of the whole body.
_~ Phosphorus occurs in combination,—as in the neutral
phosphate of sodium in the blood and saliva, the acid
phosphates of the muscles and urine, the basic phosphates
of calcium and magnesium in the bones and teeth.

Sulphur is present chiefly in the sulphocyanide of potas-
sium of the saliva, and in the sulphates of the urine and
sweat. : ,

A very small quantity of silica exists, according to
Berzelius, in the urine, and, according to others, in the
blood. Traces of it have also been found in bones, in hair,
and in some other parts of the body.

Chlorine is abundant in combination with sodium, potas-
sium, and other bases in all parts, fluid as well as solid, of
the body. A minute quantity of fluorine in combination
with calcium has been found in the bones, teeth, and
urine.

Potassium and sodium are constituents of the blood and
all the fluids, in various quantities and proportions. They
exist in the form of chlorides, sulphates, and phosphates,
and probably, also, in combination with albumen, or certain
organic acids. Liebig, in his work on the Chemistry of
Food, has shown that the juice expressed from muscular

C

18 CHEMICAL COMPOSITION OF HUMAN BODY.

flesh always contains a much larger proportion of potash-
salts than of soda-salts; while in the blood and other
fluids, except the milk, the latter salts always preponderate
over the former; so that, for example, for every 100 parts
of soda-salts in the blood of the chicken, ox, and horse,
there are only 40°8, 5°9, and 9°5 parts of potash-salts ; but
for every 100 parts of soda-salts in their muscles, there
are 381, 279, and 285 parts of potash-salts.

The salts of calcium are by far the most abundant of the
earthy salts found in the human body. They exist in the
lymph, chyle, and blood, in combination with phosphoric
acid, the phosphate of calcium being probably held in solu-
tion by the presence of phosphate of sodium. Perhaps no
tissue is wholly void of phosphate of calcium; but its
especial seats are the bones and teeth, in which, together
with carbonate and fluoride of calcium, it is deposited
in minute granules, in a peculiar compound, named
bone-earth, containing 51°55 parts of lime, and 48°45 of
phosphoric acid. Phosphate of calcium, probably the
neutral phosphate, is also found in the saliva, milk, bile,
and most other secretions, and acid phosphate in the urine,
and, according to Blondlot, in the gastric fluid. |

Magnesium appears to be always associated with calcium,
but its proportion is much smaller, except in the juice
expressed from muscles, in the ashes of which magnesia
preponderates over lime.

The especial place of iron is in the hemo-globin, the
colouring-matter of the blood, of which a further account
will be given with the chemistry of the blood. Peroxyde ©
of iron is found, in very small quantities, in the ashes of
bones, muscles, and many tissues, and in lymph and chyle,
albumen of serum, fibrin, bile, and other fluids; and a
salt of iron, probably a phosphate, exists in considerable
quantity in the hair, black pigment, and other deeply
coloured epithelial or horny substances.

Aluminium, Manganese, Copper, and Lead.—It seems most

PROTOPLASM. . IG

likely that in the human body, copper, manganesium, alumi-
nium, and lead are merely accidental elements, which, being
taken in minute quantities with the food, and not excreted
at once with the feeces, are absorbed and deposited in some
tissue or organ, of which, however, they form no necessary

part. In the same manner, arsenic, being absorbed, may

be deposited in the liver and other parts.

CHAPTER III.
STRUCTURAL COMPOSITION OF THE HUMAN BODY.

In the investigation of the structural composition of the
human body, it will be well to consider in the first place,
what are the simplest anatomical elements which enter
into its formation, and then proceed to examine those
more complicated tissues which are produced by their
union.

It may be premised, that in all the living parts of all
living things, animal and vegetable, there is invariably to
be discovered, entering into the formation of their anato-
mical elements, a greater or less amount of a substance,
which, in chemical composition and general characters, is
indistinguishable from albumen. As it exists, in a living
tissue or organ, it differs essentially from mere albumen
in the fact of its possessing the power of growth, develop-
ment, and the like; but in chemical composition it is
identical with it.

This albuminous substance has received various names
according to the structures in which it has been found, and

the theory of its nature and uses which may have pre-
c2

20 STRUCTURAL COMPOSITION OF HUMAN BODY.

sented itself most strongly to the minds of its observers.
In the bodies of the lowest animals, as the Rhizopoda or
Gregarinida, of which it forms the greater portion, it has
been called ‘‘ sarcode,” from its chemical resemblance to the
flesh of the higher animals. When discovered in vegetable
cells, and supposed to be the prime agent in their con-
struction, it was termed “‘ protoplasm.” As the presumed
formative matter in animal tissues it was called ‘‘ blastema;”’
and, with the belief that wherever found, it alone of all
matters has to do with generation and nutrition, Dr. Beale
has surnamed it ‘‘ germinal matter.”

So far as can be discovered, there is no difference in
chemical composition between the protoplasm of one part or
organism and that of another. The movements which can
* be seen in certain vegetable cells apparently belong to a sub-
stance which is identical in composition with that which
constitutes the greater portion of the bodies of the lowest
animals, and which is present in greater or less quantity
in all the living parts of the highest. So much appears
to be a fact ;—that in all living parts there exists an albu-
minous substance, in which in favourable cases for observa-
tion in vegetable and the lower animal organisms, there
can be noticed certain phenomena which are not to be
accounted for by physical impressions from without, but
are the result of inherent properties we call vital. For
example, if a hair of the Tradescantia Virginica, or of
many other plants, be examined under the microscope,
there is seen in each individual cell a movement of the pro-
toplasmic contents in a certain definite direction around the
interior of the cell. Each cell is a closed sac or bag, and its
contents are therefore quite cut off from the direct influence
of any motive power from without. The motion of the
particles, moreover, in a circuit around the interior of the
cell, precludes the notion of its being due to any other
than those molecular changes which we call vital. Again,
in the lowest animals, whose bodies resemble more than

PROTOPLASM. } 21

anything else a minute mass of jelly, and which appear
to be made up almost solely of this albuminous protoplasm,
there are movements in correspondence with the needs of
the organism, whether with respect to seizing food
or any other purpose, which are unaccountable accord-

vital. In many, too, “there is a kind of molecular cur- |
rent, exactly arasecsicam: that which is seen in a vegetable |
cell.

In the higher animals, phenomena such as these are so
subordinate to the more complex manifestations of life that
they are apt to be overlooked; but they exist nevertheless.
The mere nutrition of each part of the body in man or in
the higher animals, is performed after a fashion which is
strictly analogous to that which holds good in the case of
a vegetable cell, or a rhizopod ; or, in other words, the
life of each anatomical element in a complex structure,
like the human body, resembles very closely the life of
what in the lowest organisms constitutes the whole being.
For example, the thin scaly covering or epidermis, which
forms the outér part of a man’s skin, is made up of minute
cells, which, when living, are composed in part of pro-
toplasm, and which are continually wearing away and.
being replaced by new similar elements from beneath ;
and this process of quick waste and repair could only take
place under the very complex conditions of nutrition which
exist in man. One working part of the organism of an
animal is so inextricably interwoven with that of another,
that any want or defect in one, is soon or immediately felt
by the whole ; and the epidermis, which only subserves a
mechanical function, would be altered very soon by any
defect in the more essential parts concerned in circulation,
respiration, &c. But if we take simply the life-history
of one of the small cells which constitute the epidermis,
we find that it absorbs nourishment from the parts around,
grows, and developes in a manner analogous to that which

22 STRUCTURAL COMPOSITION OF HUMAN BODY.

belongs to a cell which constitutes part of a vegetable
structure, or even a cell which by itself forms an indepen-
dent being. |

Remembering, however, the invariable presence of a
living albuminous matter or protoplasm of apparently
identical composition in all living tissues, animal and
vegetable, we must not forget that its relations to the
parts with which it is incorporated are still very doubtfully
known; and all theories concerning it must be considered
only tentative and of uncertain stability.

Among the anatomical elements of the human body,
some appear, even with the help of the best microscopic
apparatus, perfectly uniform and simple: they show no trace
of structure, z.¢., of being composed of definitely arranged
dissimilar parts. These are named simple, structureless, or
amorphous substances. Such is the simple membrane which
forms the walls of most primary cells, of the finest gland-
ducts, and of the sarcolemma of muscular fibre; and such |
is the membrane enveloping the vitreous humour of the
eye. Such also, having a dimly granular appearance,
but no really granular structure, is the intercellular sub-
stance of the so-called hyaline cartilage.

In the parts which present determinate structure, certain
primary forms may be distinguished, which, by their
various modifications and modes of combination make up
the tissues and organs of the body. Such are, I. Gra-
nules or molecules, the simplest and minutest of the primary
forms. ‘They are particles of various sizes, from immea-
surable minuteness to the 10,000th of an inch in diameter;
of various and generally uncertain composition, but usually
so affecting light transmitted through them, that at dif-
ferent focal distances their centre, or margin, or whole
substance, appears black. From this character, as well as
from their low specific gravity (for in microscopic examina-
tions they always appear lighter than water), and from
their solubility in ether when they can be favourably

NUCLEI. 23

tested, it is probable that most granules are formed of
fatty or oily matter; or, since they do not coalesce as
minute drops of oil would, that they are particles of oil
coated over with albumen deposited on them from the -
fluid in which they float. In any fluid that is not too
viscid, they exhibit the phenomenon of molecular motion,
shaking and vibrating incessantly, and sometimes moving
through the fluid, probably, in great measure, under the
influence of external vibration.

Granules may be either free, as in milk, chyle, milky
serum, yelk-substance, and most tissues containing cells
with granules; or enclosed, as are the: granules in
nerve-corpuscles, gland-cells, and epithelium-cells, the
pigment granules in the pigmentum nigrum and me-
dullary substance of the hair; or imbedded, as are the
granules of phosphate and carbonate of lime, in bones and
teeth.

_ 2. Nuclei, or cytoblasts (fig. 1, 6), appear to be the simplest
elementary structures, next to granules. They were thus -
named in accordance with the hypothesis that they are
always connected with cells, or tissues formed from cells,
and that in the development of these, each nucleus is the
germ or centre around which the cell is formed. The
hypothesis is only partially true, but the terms based on it
are too familiarly accepted to make it advisable to change
them till some more exact and comprehensive theory is
formed. |

Of the corpuscles called nuclei some are minute cellules
or vesicles, with walls formed of simple membrane, enclos-
ing often one or more particles, like minute granules,
called nucleoli (fig. 1,'c). Other nuclei, again, appear to
be simply small masses of protoplasm, with no trace of
vesicular structure.

One of the most general characters of the nucleus, and
the most useful in microscopic examinations, is, that it is
neither dissolved nor made transparent by acetic acid, but

24 STRUCTURAL COMPOSITION OF HUMAN BODY.

acquires, when that fluid is in contact with it, a darker and
more distinct outline. It is commonly, too, the part of the
mature cell which is capable of being stained by an ammo-
niacal solution of carmine—the test, it may be remarked,

by which, according to Dr. Beale, protoplasm or germinal
matter may be always known.

Nuclei may be either free or attached. ree nuclei are
such as either float in fluid, like those in some of the secre-
tions, which appear to be derived from the secreting cells
of the glands, or lie loosely embedded in solid substance, as
in the grey matter of the brain and spinal cord, and most
abundantly in some quickly-growing tumours. Aiétached
nuclet are either closely imbedded in homogeneous pellucid
substance, as in rudimental cellular tissue ; or are fixed on
the surface of fibres, as on those of organic muscle and
organic nerve-fibres ; or are enclosed in cells, or in tissues
formed by the extension or junction of cells. Nuclei en-
closed in cells appear to be attached to the inner surface of
the cell-wall, projecting into the cavity. . Their position in
relation to the centre or axis of the cell is uncertain; often
when the cell lies on a flat or broad surface, they appear
central, as in blood corpuscles, epithelium-cells, whether
tesselated or cylindrical; but, perhaps, more often their
position has no regular relation to the centre of the cell.
In most instances, each cell contains only a single nucleus;
but in cartilage, especially when it is growing or ossifying,
two or more nuclei in each cell are common; and the
development of new cells is often effected. by a division or
multiplication of nuclei in the cavity of a parent cell; as in

the primary blood-cells of the embryo in the germinal

vesicle, and others.

When cells extend and coalesce, so that their walls form
tubes or sheaths, the nuclei commonly remain attached to
the inner surface of the wall. Thus they are seen imbedded
n the walls of the minutest capillary blood-vessels of, for
example, the retina and brain; in the sarcolemma of

at ert’ ela

pi sosieke Ere

CELLS. 26

_ transversely striated muscular fibres; and in minute gland-
tubes.

Nuclei are most commonly oval or round, and do not
generally conform themselves to the diverse shapes which
the cells assume; they are altogether less variable ele-
ments, even in regard, to size, than the cells are, of which
fact one may see a good example in the uniformity of the
nuclei in cells so multiform as those of epithelium. . But
sometimes they appear to be developed into filaments,
elongating themselves and becoming solid, and uniting
end.to end for greater length, or by lateral branches to
form a network. So, according to Henle, are formed the
filaments of the striated and fenestrated coats of arteries;
and, according to Beale, the so-called connective tissue cor-
puscles are to be considered branched nuclei, formed of
protoplasm or germinal matter.

3. Cells.—The word ‘‘ cell’’ of course implies strictly a
hollow body, and the term was a sufficiently good one
when all so-called cells were considered to be small bags
with a membranous envelope, and more or less liquid
contents. Mathy bodies, however, which are still called
cells do not answer to this description, and the term, there-
fore, if taken in its literal signification, is very apt to lead
astray, and, indeed, very frequently does so. It is too
widely used, however, to be given up, at least for the
present, and we must therefore consider the term to indi-
cate, either a membranous closed bag with more or less liquid
contents, and almost always a nucleus; or a small semi-
solid mass of protoplasm, with no more definite boundary-
wall than such as has been formed by a condensation of its
outer layers, but with, most commonly, a small granular
substance in the centre, called, as in the first place, a
nucleus. In both cases the nucleus may contain a nucleolus.
Fat cells (fig. 11) are examples of the first kind of cells ;
white blood-corpuscles (fig. of the second.

The cell-wall, when there one, never presents any

26 STRUCTURAL COMPOSITION OF HUMAN BODY.

appearance of structure: it appears sometimes to be an
albuminous substance; sometimes a horny matter, as in
thick and dried cuticle. In almost all cases (the dry cells of
horny tissue, perhaps, alone excepted) the cell-wall is made
transparent by acetic acid, which also penetrates into the
interior and distends it, so that it can hardly be discerned.
But in such cases the cell-wall is usually not dissolved ; it
may be brought into view again by merely neutralizing
the acid with soda or potash.

The simplest shape of cells, and that which is prokably
the normal shape of the primary cell, is oval or spheroidal,
as in cartilage-cells and lymph-corpuscles; but in many in-
stances they are flattened and discoid, as in the red blood-
corpuscles (fig. 26) or scale-like, as in the epidermis and
tesselated epithelium (fig. 2). By mutual pressure they
may become many-sided, as are most of the pigment-cells
of the choroidal pigmentum nigrum (fig. 12), and those
in close-textured adipose tissue; they may assume a conical
or cylindriform or prismatic shape, as in the varieties of
cylinder-epithelium (fig. 4); or be caudate, as in certain
bodies in the spleen; they may send out exceedingly fine
processes in the form of vibratile cilia (fig. 6), or larger
processes, with which they become stellate, or variously
caudate, as in some of the ramified pigment-cells of the
choroid coat of the eye (fig. 13).

The contents of all living cells, including the nucleus, are
formed in a greater or less degree of protoplasm,—less as
the cell grows older. But, besides, cells contain matters
almost infinitely various, according to the position, office,
and age of the cell. In adipose tissue they are the oily
matter of the fat; in gland-cells, the contents are the
proper substance of the secretion, bile, semen, &c., as the
case may be; in pigment-cells they are the pigment-gra-
nules that give the colour; and in the numerous instances
in which the cell-contents can be neither seen because they
are pellucid, nor tested because of their minute quantity,

INTERCELLULAR SUBSTANCE. 27

they are yet, probably, peculiar in each tissue, and con-
stitute the greater part of the proper substance of each.
Commonly, when the contents are pellucid, they contain
granules which float in them; and when water is added
and the contents are diluted, the granules display an active
molecular movement within the cavity of the cell. Such
a movement may be seen by adding water to mucus-, or
granulation-corpuscles, or to those of lymph. In a few
cases, the whole cavity of the cell is filled with granules:
it is so in yelk-cells and milk-corpuscles, in the large
diseased corpuscles often found among the products of
inflammation, and in some cells when they are the seat of
extreme fatty degeneration. All cells containing abundant
granules appear to be either lowly organized, as for nutri-
ment, ¢.g., yelk-cells, or degenerate, ¢.g., granule-cells of
inflammation, or of mucus. The peculiar contents of cells
may be often observed to accumulate first around or di-
rectly over the nuclei, as in the cells of black pigment, in
those of melanotic tumours, and in those of the liver during
- the retention of bile.

Intercellular*substance is the material in which, in certain
tissues, the cells are imbedded. Its quantity is very
variable. In the finer epithelia, especially the columnar
epithelium on the mucous membrane of the intestines, it
can be just seen filling the interstices of the close-set cells;
here it has no appearance of structure. In cartilage and
bone, it forms a large portion of the whole substance of
the tissue, and is either homogeneous and finely granular
(fig. 14), or osseous, or, as in fibro-cartilage, resembles fine
fibrous tissue (fig. 15). In some cases, the cells are very
loosely connected with the intercellular substance, and may
be nearly separated from it, as in fibro-cartilage: but in
some their walls seem amalgamated with it.

The foregoing may be regarded as the simplest, and the
nearest to the primary forms assumed in the organization
of animal matter; as the states into which this passes in

28 - STRUCTURAL COMPOSITION OF HUMAN BODY.

becoming a solid tissue living or capable of life. By the
further development of tissue thus far organized, higher or
secondary forms are produced, which it will be sufficient in
this place merely to enumerate. Such are,

4. Filaments, or jfibrils—Threads of exceeding fineness,
from 5;1,,th of an inch upwards. Such filaments are
cylindriform, as are those of the striated muscular and
the fibro-cellular or areolar tissue (fig. 8); or flattened, as
are those of the organic muscles. Filaments usually lie |
in parallel fasciculi, as in muscular and tendinous tissues ;
but in some instances are matted or reticular with branches
and intercommunication, as are the filaments of the middle
coat, and of the longitudinally-fibrous coat of arteries; and
in other instances, are spirally wound, or very tortuous, as
in the common fibro-cellular-tissue (fig. 9).

5. Fibres in the instances to which the name is commonly
applied are larger than filaments or fibrils, but are by no
essential general character distinguished from them. The
flattened band-like fibres of the coarser varieties of organic
muscle or elastic tissue (fig. 10) are the simplest examples
of this form; the toothed fibres of the crystalline lens are
more complex; and more compound, so as hardly to permit
of being classed as elementary forms, are the striated mus-
cular fibres, which consist of bundles of filaments enclosed
in separate membranous sheaths, and the cerebro-spinal
nerve-fibres, in which similar sheaths enclose apparently
two varieties of nerve substance.

6. Tubules are formed of simple, or structureless mem-
brane, such as the investing sheaths of striated muscular
and cerebro-spinal nerve-fibres, and the basement mem-
brane or proper wall of the fine ducts of secreting glands;
or they may be formed, as in the case of the minute capil-
lary lymph and blood-vessels, by the apposition, edge to
edge, in a single layer, of. variously shaped flattened cells
(fig. 48).

With these simple materials, the various parts of the

Yo 7 ——— ————————

EPITHELIUM. 29

s

body are built up; the more elementary tissues being, so |

to speak, first compounded of them; while these again
are variously mixed and interwoven to form more intricate
combinations. Thus are constructed epithelium and its
modifications, connective tissue, fat, cartilage, bone, the
fibres of muscle and nerve, etc. ; and these again, with the
more simple structures before mentioned, are used as mate-
rials wherewith to form arteries, veins, and lymphatics,
secreting and vascular glands, lungs, heart, liver, and other
parts of the body.

CHAPTER IV.*
STRUCTURE OF THE ELEMENTARY TISSUES.

Epithelium.

OnE of the simplest of the elementary structures of which
the human body is made up, is that which has received the
name of Epithelium. Composed of nucleated cells which are
arranged most commonly in the form of a continuous
membrane, it lines the free surfaces both of the inside and
outside of the body, and its varieties, with one exception,
have been named after the shapes which the individual
cells in different parts assume. Classified thus, Epithelium
presents itself under four principal forms, the characters
of each of which are distinct enough in well-marked ex-
amples; but when, as frequently happens, a continuous

* The following Chapter, containing an outline-description of the
elementary tissues, has been inserted for the convenience of students.
For a much fuller and better account, the reader may be referred to
Dr, Sharpey’s admirable descriptions in Quain’s Anatomy.

’

lye ELEMENTARY TISSUES.

surface possesses at different parts two or more different
epithelia, there is a very gradual transition from one to the
other.

1. The first and most common variety is the squamous
or tesselated epithelium (figs. I and 2), which is composed
of flat, oval, roundish, or polygonal nucleated cells, of
various size, arranged in one, or in many superposed
layers. Arranged in several superposed layers this form of

Fig. 1.* Fig. 2.*

epithelium covers the skin, where it is called the Epidermis,
and is spread over the mouth, pharynx, and csophagus,
the conjunctiva covering the eye, the vagina, and entrance
of the urethra in both sexes; while, as a single layer the
same kind of epithelium lines the interior of most of the
serous and synovial sacs, and of the heart, blood-vessels,
and lymph-vessels. é

2. Another variety of epithelium named spheroidal, from
the usually more or less rounded outline of the cells com-

* Fig. 1. Fragment of epithelium from a serous membrane (peri-
toneum) ; magnified 410 diameters. a. cell; 0. nucleus; c. nucleoli
(Henle).

+ Fig. 2. Epithelium scales from the inside of the mouth ; magnified
260 diameters (Henle).

Se

ee ot
ee Se

see 2s

fe dt

EPITHELIUM. 31

posing it (d, fig. 3), is found chiefly lining the interior of the
ducts of the compound glands, and more or less completely
filling the small sacculations or acini, in which they ter-
minate. It commonly indeed occupies the true secreting
parts of all glands, and hence is sometimes called glandular
epithelium (b,c, and d, fig. 3). Often, from mutual pressure,

Fig. 3.* *

the cells acquire a polygonal outline. From the fact, how-
ever, of the term spheroidal epithelium being a generic one
for almost all gland-cells, the shapes and sizes of the cells
composing this variety of epithelium are, as might be ex-
pected, very diverse in different parts of the body.

3. The third variety is the cylindrical or columnar

* Fig. 3. The gastric glands of the human stomach (magnified).
a, deep part of a pyloric gastric gland (from Kolliker) ; the cylindrical
epithelium is traceable to the cecal extremities. 06 and ¢, cardiac
gastric glands (from Allen Thomson) ; 8, vertical section of a small
portion of the mucous membrane with the glands magnified 30 diameters ;
ce, deeper portion of one of the glands, magnified 65 diameters, showing
a slight division of the tubes, and a sacculated appearance produced by
the large glandular cells within them ; d, cellular elements of the cardiac
glands magnified 250 diameters.

32 ELEMENTARY TISSUES.

epithelium (figs. 4 and 5), which extends from the cardiac

orifice of the stomach along the whole of the digestive
canal to the anus, and lines the principal gland-ducts which

open upon the mucous surface of this tract, sometimes
throughout their whole extent (a, fig. 3), but in some cases
only atthe part nearest to the orifice (o and). It is also

Fig. 5.+

Mir, By oe Sait

found in the gall-bladder and in the greater portion of the
urethra, and in some other parts, as the duct of the parotid
gland and of the testicle. It is composed of oblong cells
closely packed, and placed perpendicularly to the surface
they cover, their deeper or attached extremities being most

* Fig. 4. Cylindrical epithelium from intestinal villus of a rabbit ;
magnified 300 diameters (from Kolliker).

{ Fig. 5. Cylinders of the intestinal epithelium (after Henle) :—
B. from the jejunum; c. cylinders of the intestinal epithelium as
seen when looking on their free extremities ; D. ditto, as seen ona
transverse section of a villus.

a OG REP TS Pt

oad: up egy ok nial ws

ep eg

x
By
a

ea eee

&

~

_

dy he Re

EPITHELIUM. 33

commonly smaller than those which are free. Each of such
cells encloses, at nearly mid distance between its base and
apex, a flat nucleus with nucleoli (x, fig. 5); the nuclei
being arranged at such heights in contiguous cells as not
to interfere with each other by mutual pressure. |

4. The fourth variety of epithelium cells, usually
cylindrical, but occasionally of some other shape, are pro-
vided at their free extremities with several fine pellucid
pliant processes or cilia (figs. 6 and 7). This form of epi-
thelium lines the whole respiratory tract of mucous mem-
brane and its prolongations. It occurs also in some parts

Fig. 6.*

of the generative apparatus; in the male, lining the vasa
efferentia of the testicle, and their prolongations as far as
the lower end of the epididymis; and, in the female com-
mencing about the middle of the neck of the uterus, and ex-
tending to the fimbriated extremities of the Fallopian tubes,
_ and for a short distance along the peritoneal surface of the
latter. A tesselated epithelium, with scales partly covered
with cilia, lines, in great part, the interior of the cerebral
ventricles,

If a portion of ciliary mucous membrane from a living or
recently dead animal be moistened and examined with a
microscope, the cilia are observed to be in constant motion,

* Fig. 6. Spheroidal ciliated cells from the mouth of the frog ;

magnified 300 diameters (Sharpey).
+ Fig. 7. Columnar ciliated epithelium cells from the human nasal
membrane ; magnified 300 diameters (Sharpey).
D

34 ELEMENTARY TISSUES.

moving continually backwards and forwards, and alter-
nately rising and falling with a lashing or fanning
movement. The appearance is not unlike that of the
waves in a field of corn, or swiftly running and rippling
water. The general result of their movements is to pro-
duce a continuous current in a determinate direction, and
this direction is invariably the same on the same surface,
being usually in the case of a cavity towards its external
orifice.

Uses of Epithelium.—The various kinds of epithelium
serve one general purpose, namely, that of protecting, and
at the same time rendering smooth, the surfaces on which
they are placed. But each, also, discharges a special office
in relation to the particular function of the membrane on
which it is placed.

In mucous and synovial membranes it is highly probable

_ that the epithelium-cells, whatever be their forms and what-
ever their other functions, are the organs in which by a
regular process of elaboration and secretion, such as will be
afterwards described, mucus and synovial fluid are formed
and discharged. (See chapter on Secretion).

Ciliated epithelium has another superadded function. By
means of the current set up by its cilia in the air or fluid
in contact with them, it is enabled to propel the fluids
or minute particles of solid matter, which come within
the range of its influence, and aid in their expulsion
from the body. In the respiratory tract of mucous mem-
brane the current set up in the air may also assist in
the diffusion and change of gases, on which the due
aération of the blood depends. In the Fallopian tube
the direction of the current excited by the cilia is towards
the cavity of the uterus, and may thus be of service in
aiding the progress of the ovum. Of the purposes served
by the cilia which line the ventricles of the brain nothing
is known.

The nature of ciliary motion and the circumstances by

AREOLAR TISSUE. 35

which it is influenced will be considered hereafter. (See
chapter on Motion.)

Epithelium is devoid of blood-vessels, and lymphatics.
The cells composing it are nourished by absorption of
nutrient matter from the tissues on which they rest; and
as they grow old they are cast off and replaced by new cells
from beneath.

Areclar, Cellular, or Connective Tissue.

This tissue, which has received various names according
to the qualities which seemed most important to the authors
who have described it, is met with in some form or otherin
every region of the body; the areolar tissue of one dis-
trict being, directly or indirectly, continuous with that of

Fig. 8.*

all others. In most parts of the body this structure 2
contains fat, but the quantity of the latter is very variable,
and in some few regions it is absent altogether (p. 38).

« Fig. 8. -Filaments of areolar tissue, in larger and smaller bundles,
as seen under a magnifying power of 400 diameters (Sharpey).
D 2

36 ELEMENTARY TISSUES.

Probably no nerves are distributed to areolar tissue itself,
although they pass through it to other structures; and
although blood-vessels are supplied to it, yet they are
sparing in quantity, if we except those destined for the fat
which is held in its meshes.

Under the microscope areolar tissue seems composed of
a mesh-work of fine fibres of two kinds. The first, which
makes up the greater part of the tissue, is formed of very
fine white structureless fibres, arranged closely in bands and
bundles, of wave-like appearance when not stretched out,
and crossing and intersecting in all directions (fig. 8). The
' second kind, or the yellow elastic fibre (fig. 10), has a much

Fig. 9.*

sharper and darker outline, and is not arranged in bundles,
but intimately mingled with the first variety, as more or
less separate and well-defined fibres, which twist among and
around the bundles of white filaments (fig. 9). Sometimes

* Fig. 9. Magnified view of areolar tissues (from different parts)
treated with acetic acid. The white filaments are no longer seen, and
the yellow or elastic fibres with the nuclei come into view. At ¢,
elastic fibres wind round a bundle of white fibres, which, by the effect

ofthe acid, is swollen out between the turns, Some connective tissue.

corpuscles are indistinctly represented in c (Sharpey).

Ee ee ee ee ee

AREOLAR TISSUE. 37

the yellow fibres divide at their ends and anastomose with
each other by means of the branches. Among the fibrous
parts of areolar or connective tissue are little nuclear
bodies of various shapes, called connective-tissue corpuscles
(fig. 9, c.), some of which are prolonged at various points
of their outline into small processes which meet and join
others like them proceeding from their neighbours.

The chief functions of areolar tissue seem to consist in
the investment and mechanical support of various parts,
and as a connecting bond between such structures as may
need it. The connective-tissue corpuscles, which, accord-
ing to Beale, are small branched particles of germinal
matter or protoplasm, probably minister to the nutrition of
the texture in which they are seated.

In various parts of the body,
each of the two constituents of
areolar tissue which have been
just mentioned, may exist sepa-
rately, or nearly so. ‘Thus ten-
dons, fascize, and the like more
or less inelastic structures, are
formed almost exclusively of the
white fibrous tissue, arranged ac-
cording to the purpose required,
either. in parallel bundles or
membraneous meshes; while the
yellow elastic fibres are found to
make up almost alone such elas-
tic structures as the vocal cords,
the ligamenta subflava, etc., and
to enter largely into the composition of the blood-vessels,
the trachea, the lungs, and many other parts of the body.

Fig. 10.*

* Fig. 10. Elastic fibres from the ligamenta subflava, magnified
about 200 diameters (Sharpey).

38 ELEMENTARY TISSUES.

Adipose Tissue.

In almost all regions of the human body a larger or
smaller quantity of adipose or fatty tissue is present; the
chief exceptions being the subcutaneous tissue of the eye-
lids, penis and scrotum, the nymphe and the cavity of
the cranium. Adipose tissue is also absent from the sub-
stance of many organs, as the lungs, liver and others.

Fatty matter, not in the form of a distinct tissue, is also
widely present in the body, as the fat of the liver and
brain, of the blood and chyle, ete.

Adipose tissue is almost always found seated in areolar
tissue, and forms in its meshes little masses of unequal
size and irregular shape, to which the term, lobules, is
commonly applied. Under the, microscope it is found to

Fig. 11.*

consist essentially of little vesicles or cells about =1,th or
toth of an inch in diameter, each composed of a struc-
tureless and colourless membrane or bag, filled with fatty
matter which is liquid during life, but in part solidified
after death. A nucleus is always present in some part or
other of the cell-walli ; but in the ordinary condition of the

* Fig. 11. A small cluster of fat-cells; magnified 150 diameters
(Sharpey).

PIGMENT-CELLS. 39

cell it is not easily or always visible. The ultimate cells are

held together by capillary blood-vessels; while the little
clusters thus formed are grouped into small masses, and
held so, in most cases, by areolar tissue. The oily matter
contained in the cells is composed chiefly of the compounds
of fatty acids with glycerin, which are named olein, stearin,
and palmitin.

It is doubtful whether lymphatics or nerves are supplied
to fat, although both pass through it on their way to other
structures.

Among the uses of fat, these seem to be the chief :—

1. It serves as a store of combustible matter which
may be re-absorbed into the blood when occasion re-
quires, and being burnt, may help to preserve the heat of
the body.

2. That part of the fat which is situate beneath the skin
must, by its want of conducting power, assist in preventing
undue waste of the heat of the body by escape from the
surface.

3. As a packing material, fat serves very admirably to
fill up spaces, to form a soft and yielding yet elastic mate-
rial wherewith to wrap tender and delicate structures, or
form a bed with like qualities on which such structures
may lie, unendangered by pressure. As good examples of
situations in which fat serves such purposes may be men-
tioned the palms of the hands, and soles of the feet, and
the orbits.

4. In the long bones, fatty tissue, in the form known as
marrow, serves to fill up the medullary canal, and to sup-
port the small blood-vessels which are distributed from it
to the inner part of the substance of the bone.

Pigment.
In various parts of the body there exists a considerable

quantity of dark pigmentary matter, ¢.g., in the choroid
coat of the eye, at the back of the iris, in the skin, etc.

40 . ELEMENTARY TISSUES.

In all these cases the dark colour is due tothe presence of
so-called pigment-cells. |

Pigment-cells are for the most part polyhedral (fig. 12)
or spheroidal, although sometimes they have irregular
processes, as shown in fig. 13. The cell-wall itself is
colourless,—the dark tint being produced by small dark
granules heaped closely together, and more or less con-
cealing the nucleus, itself colourless, which each cell
contains. The dark tint of the skin, in those of dark com-
plexion and in the coloured races, is seated chiefly in the

Fig. 12.* Fig. 13.

epidermis, and depends on the presence of pigment-cells,

which, except in the presence of the dark granules in their

interior, closely resemble the colourless cells with which
they are mingled. The pigment-cells are situate chiefly in
the deep layer of the epidermis, or the so-called rete
mucosum. (See chapter on the Skin.)

* Fig. 12. Pigment-cells from the choroid ; magnified 370 diameters.

(Henle). A, cells still cohering, seen on their surface ; a, nucleus
indistinctly seen. In the other cells the nucleus is concealed by the

pigment granules. B, two cells seen in profile ; a, the outer or posterior

part containing scarcely any pigment.

+ Fig. 13. Ramified pigment cells, from the tissue of the choroid
. coat ofthe eye ; magnified 350 diameters (after Kolliker). a, cells with
pigment ; 4, colourless fusiform cells.

%
=
4
E
,
i
§
‘
:
‘
5
s

ee ee ee ne Pa

CARTILAGE, | Cp ae

The pigmentary matter is a very insoluble compound
of carbon, hydrogen, nitrogen and oxygen,—the carbon
largely predominating ; besides, there is a small quantity
of saline matter.

The uses of pigment in most parts of the body are not
clear. In the eyeball it is evidently intended for the
absorption of superfluous rays of light.

Cartilage.

Cartilage or gristle exists in different forms in the
human body, and has been classified under two chief
heads, namely, temporary and permanent cartilage; the
former term being applied to that kind of cartilage which,
in the foetus and in young subjects, is destined to be con-
verted into bone. The varieties of permanent cartilage
have been arranged in three classes, namely, the cellular,
the hyaline, and the jibrous cartilages,—the last-named,
being again capable of subdivision into two kinds,
namely, elastic or yellow cartilage, and the so-called jibro-
cartilage.

Elastic cartilage, however, contains fibres, and fibro-
cartilage is more or less elastic; it will be well, therefore,
for distinction’s sake to term those two kinds white fibro-
cartilage and yellow fibro-cartilage respectively.

The accompanying table represents the classification of
the varieties of cartilage :—

1. Temporary.
A. Cellular.
B. Hyaline.
nee White fibro-cartilage.
C. Fibrous: Yellow fibro-cartilage.

2. Permanent.

All kinds of cartilage are composed of cells imbedded
in a substance ealled the matrix: and the apparent
differences of structure met with in the various kinds of
cartilage are more due to differences in the character of
the matrix than of the cells. Among the latter, however,
there is also considerable diversity of form and size.

42 ELEMENTARY TISSUES.

With the exception of the articular variety, cartilage is
invested by a thin but tough and firm fibrous membrane
called the perichondrium. On the surface of the articular
cartilage of the foetus, the perichondrium is represented by
a film of epithelium; but this is gradually worn away up
to the margin of the articular surfaces, when by use the
parts begin to suffer friction.

1. Cellular cartilage may be readily obtained from the
external ear of rats, mice, or other small mammals. It is
composed almost entirely of cells (hence its name), with little
or no matrix. The latter, when present, consists of very fine
fibres, which twine about the cells in various directions and
enclose them in a kind of network. The cells are packed
very closely together,—so much so that it is not easy in all
cases to make out the fine fibres often encircling them.

Cellular cartilage is found in the human subject, only
in early foetal life, when it
constitutes the Chorda dor-
salis. (See chapter on Genera-
tion.)
~ 2. Hyaline cartilage is met
with largely in the human
body,—investing the articular
ends of bones, and forming
the costal cartilages, the nasal
'Y cartilages, and those of the
larynx, with the exception of
the epiglottis and cornicula
laryngis. Like other cartilages it is composed of cells
imbedded in a matrix (fig. 14). _

Fig. 14.*

_ * Fig. 14. A thin layer peeled off from the surface of the cartilage
of the head of the humerus, showing flattened groups of cells. The

shrunken cell-bodies are distinctly seen, but the limits of the capsular

cavities, where they adjoin one another, are but faintly indicated.
Magnified 400 diameters (after Sharpey).

Of ti eel

nigeria hh

er a te. uy Me ee, ee or and

4S p>

9h elie pes

CARTILAGE. 43

The cells, which contain a nucleus with nucleoli, are
irregular in shape, and generally grouped together in
patches. The patches are of various shapes and sizes, and
placed at unequal distances apart. They generally appear
flattened near the free surface of the mass of cartilage in
which ‘they are placed, and more or less perpendicular to
the surface in the more deeply seated portions.

The matrix in which they are imbedded has a dimly
granular appearance, like that of ground glass.

In the hyaline cartilage of the ribs, the cells are mostly
larger than in the articular variety, and there is a tendency
to the development of fibres in the matrix. The costal
cartilages also frequently become ossified in old age, as
also do some of those of the larynx.

Temporary cartilage closely resembles the ordinary
hyaline kind; the cells, however, are not grouped together
after the fashion just described, but are more uniformly
distributed throughout the matria.

Articular hyaline cartilage is reckoned among the so-
called non-vascular structures, no blood-vessels being sup-
plied directly to its own substance; it is nourished by
those of the bone beneath. When hyaline cartilage is in
thicker masses, as in the case of the cartilages of the ribs,
a few blood-vessels traverse its substance. The distinction,
however, between all so-called vascular and non-vascular
parts, is at the best a very artificial one. (See chapter on
Nutrition. ) |

Nerves are probably not supplied to any variety of
cartilage.

Fibrous cartilage, as before mentioned, occurs under two
chief forms, the yellow and the white fibro-cartilage.

Yellow fibro-cartilage is found in the external ear, in the
epiglottis and cornicula laryngis, and in the eyelid. The
cells are rounded or oval, with well-marked nuclei and
nucleoli. The matrix in which they are seated is composed
almost entirely of fine fibres, which form an intricate inter-

~

Aa ELEMENTARY TISSUES.

lacement about the cells, and in their general characters
are allied to the yellow variety of fibrous tissue (fig. 15).

White fibro-cartilage, which
is much more widely distri-
buted throughout the body,
than the foregoing kind, is
- composed, like it, of cells and
a matrix; the latter, however,
being made up almost entirely
of fibres closely resembling
those of white fibrous tissue.

In this kind of fibro-car-
tilage it is not unusual to find a great part of its mass
composed almost exclusively of fibres, and deserving the
name of cartilage only from the fact that in another por-
tion, continuous with it, cartilage cells may be pretty freely
distributed.

The different situations in which white fibro-cartilage is
formed have given rise to the following classification :—

1. Inter-articular fibro-cartilage, e.g., the semilunar car-
tilages of the knee-joint.

2. Circumferential or marginal, as on the edges of the
acetabulum and glenoid cavity of the scapula.

3. Connecting, e.g., the inter-vertebral fibro-cartilages.

4. Fibro-cartilage is found in the sheaths of tendons,
and sometimes in their substance. In the latter situation,
the nodule of fibro-cartilage is called a sesamoid fibro-carti-
lage, of which a specimen may be found in the tendon of
the tibialis posticus, in the sole of the foot, and usually in
the neighbouring tendon of the peroneus longus.

The uses of cartilage are the following :—in the joints,
to form smooth surfaces for easy friction, and to act as a
buffer, in shocks; to bind bones together, yet to allow a
certain degree of movement, as between the vertebrae; to

* Fig. 15. Section of the epiglottis, magnified 380 diameters (Dr.
Baly).

BONE. | 45

form a firm framework and protection, yet without undue
stiffness or weight, as in the larynx and chest walls; to
deepen joint-cavities, as in the acetabulum, yet not so as
to restrict the movements of the bones; to be, where such
qualities are required, firm, tough, flexible, elastic, and
strong. et
Structure of Bones and Teeth.

Bone is composed of earthy and animal matter in the
proportion of about 67 per cent. of the former to 33 per
cent. of the latter. The earthy matter is composed chiefly
of phosphate of lime, but besides there is a small quantity,
about 11 of the 67 per cent., of carbonate of lime, with
minute quantities of some other salts. The animal matter
is resolved into gelatine by boiling. The earthy and
animal constituents of bone are so intimately blended and
incorporated the one with the other, that it is only by
chemical action, as for instance, by heat in one case, and
by the action of acids in another, that they can be sepa-
rated. Their close union, too, is further shown by the
fact that when by acids the earthy matter is dissolved out,
or, on other Fand, when the animal part is burnt out,
the general shape of the bone is alike preserved.

To the naked eye there appear two kinds of structure
in different bones, and in different parts of the same bone,
namely, the dense or compact, and the cancellous tissue.
Thus, in making a longitudinal section of a long bone, as
the humerus or femur, the articular extremities are found
capped on their surface by a thin shell of compact bone,
while their interior is made up of the spongy or cancellous

tissue. The shaft, on the other hand, is formed almost

entirély of a thick layer of the compact bone, and this sur-

rounds a central canal, the medullary cavity—so called from

its containing the medulla or marrow (p. 39). ‘In the flat
bones, as the parietal bone or the scapula, one layer of
the cancellous structure lies between two layers of the

compact tissue, and in the short and irregular bones, as

those of the carpus and tarsus, the cancellous tissue alone

46 ELEMENTARY TISSUES.

fills the interior, while a thin shell of compact bone forms
the outside. The spaces in the cancellous tissue are filled
by a species of marrow, which differs considerably from
that of the shaft of the long bones. It is more fluid, and
of a reddish colour, and contains very few fat cells.

The surfaces of bones, except the parts covered with
articular cartilage, are clothed by a tough fibrous mem-
brane, the periosteum; and it is from the blood-vessels
which are distributed first in this membrane, that the

Fig. 16.*

Pipes : SZ,
“GZ =

\ dt
ae

bones, especially their more compact tissue, are in great
part supplied with nourishment,—minute branches from
the periosteal vessels entering the little foramina on the
surface of the bone, and finding their way to the Haversian
canals, to be immediately described. The long bones are

* Fig. 16. Transverse section of compact tissue (of humerus) mag-
nified about 150 diameters. Three of the Haversian canals are seen,
with their concentric rings ; also the corpuscles or lacune, with the
canaliculi extending from them across the direction of the lamelle. The
Haversian apertures had got filled with débris in grinding down the
section, and therefore appear black in the figure, which represents the
object as viewed with transmitted light (after Sharpey).

a oe a ee ee ee sth Niet

on eee ee Se eee eee

yf ew oe an eee >

toa ae ia

BONE. 47

supplied also by a proper nutrient artery, which entering
at some part of the shaft so as to reach the medullary
canal, breaks up into branches for the supply of the marrow,
from which again small vessels are distributed to the inte-
rior of the bone. Other small blood-vessels pierce the arti-
cular extremities for the supply of the cancellous tissue.
Notwithstanding the differences of arrangement just
mentioned, the structure of all bone is found, under the
microscope, to be essentially the same. Examined with a
rather high power, its substance is found occupied by a
multitude of little spaces, called lacune, with very minute
’ canals or canaliculi, as they are termed, leading from them,
and anastomosing with similar little prolongations from
other lacunee (fig. 16). In very thin layers: of bone, no
other canals than these may be
visible; but on making a transverse
section of the compact tissue, ¢.g.,
of a long bone, as the humerus or
ulna, the arrangement shewn in
. fig. 16can be seen. The bone seems
mapped out into small circular dis-
tricts, at or about the centre of each
of which is a hole, and around this
an appearance as of concentric
layers—the lacune and canaliculi fol-
lowing the same concentric plan of
distribution around the small hole
in the centre, with which, indeed,
they communicate. On making a
longitudinal section, the central
holes are found to be simply the cut extremities of small
canals which run lengthwise through the bone (fig. 17), and

* Fig. 17. Haversian canals, seen in a longitudinal section of the
compact tissue of the shaft of one of the long bones. a. Arterial canal ;
b. Venous canal; ¢. Dilatation of another venous canal.

48 ELEMENTARY TISSUES.

are called Haversian canals, after the name of the physician,
Clopton Havers, who first accurately described them.

The Haversian canals, the average diameter of which
is ~1., of an inch, contain blood-vessels, and by means of
them, blood is conveyed to all, even the densest parts
of the bone; the minute canaliculi and lacunee absorbing
nutrient maiter from the Haversian blood-vessels, and con-
veying it still more intimately to the very substance of the
bone which they traverse. The blood-vessels enter the
Haversian canals both from without, by traversing the
small holes which exist on the surface of all bones beneath
the periosteum, and from within by means of small channels,
which extend from the medullary cavity, or from the can-
cellous tissue. According to Todd and Bowman, the arteries
and veins usually occupy separate canals, and the veins
which are the larger, often present, at irregular intervals,
small pouch-like dilatations (fig. 17).

The lacune are occupied by nucleated cells, or, as Dr.
Beale expresses it, minute portions of protoplasm or
germinal matter; and there is every reason to believe that
the lacunar cells are homologous with the corpuscles of
the connective tissue, each little particle of protoplasm
ministering to the nutrition of the bone immediately
surrounding it, and one lacunar particle communicating
with another, and with its surrounding district, and with
the blood-vessels of the Haversian canals, by means of
the minute streams of fluid nutrient matter which occupy
the canaliculi.

Besides the concentric lamelle of bone tissue which
surround the Haversian canal in the shaft of a long bone,
are others, especially near the circumference, which
surround the whole bone, and are arranged concentrically
with regard to the medullary canal.

The ultimate structure of the lamelig appears to be
reticular. If a thin film be peeled off the surface of a bone
from which the earthy matter has been removed by acid,

- saat

inn oe

Sar

i > ~ = 2 ait Zi " hoody ~ int a —
ee ee ee ee ee ee ee oe

i ee

/ *
iy PENRYN peal Paine Oe ok si Sa

ae) ie ”- na

ii a ie

BONE. - - 49

and examined with a high power of the microscope, it will
be found composed, according to Sharpey, of a finely
reticular structure, formed appa-
rently of very slender fibres decus-

sating obliquely, but coalescing at Up tii ie ny
the points of intersection, as if here | TE ae
the fibres were fused rather . than \ ma BRO
woven together (fig. 18). ZnS SRP
In many places these reticular Mine RCNA
lamellee are perforated by tapering PSR. ES
fibres, resembling in character the LUA AMOR
ordinary white or rarely the elastic 4 ii HN
fibrous tissue, which bolt the neigh- RWRRN DRY

bouring lamelle together, and may
be drawn out when the latter are torn asunder (fig. 19). -

Bone is developed after two different fashions. In one,
the tissue in which the earthy matter is laid down is a
membrane, composed mainly of fibres and granular cells,
like imperfectly developed connective-tissues.. Of this kind
of ossification in membrane, the flat bones of the skull
are examples. «in the other, and much more common case,
of which a long bone may be cited as an instance, the
ossification takes place in cartilage.

In most. bones ossification begins at more than one
point; and from these centres of ossification, as they are
called, the process of deposition of calcareous matter
advances in all directions. Bones grow by constant de-
velopment of. the cartilage or membrane between these
centres of ossification, until by the process of calcification
advancing at a quicker rate than the development of the
softer structures, the bone becomes impregnated through-

* Fig. 18. Thin layer peeled off from a softened bone, as it appears
under a magnifying power of 400.—This figure, which is intended to
represent the reticular structure of a lamella, gives a better idea of the
object when held rather farther off than usual from the eye (from

Sharpey).
E

50 | ELEMENTARY TISSUES.

out with calcareous matter, and can grow no more. In
the long bones the main centres of ossification are seated
at the middle of’ the shaft, and at each of the extremities.
Increase of the length of bones, therefore, occurs at the part
which intervenes between the ossifying centre in the shaft

Fig. 19.*

ry = yA >
cs
= ~
Z .
y SS
Zp, : FOISSSe
Za Z \ WSSey > yj f. x
< \ a Ne a7 / Sane AABAS 2s
se Z ro 4 Va a . ==
OE EGR 3
Le eae
y Z =>
eC J é x
S

Ups
Gy,
Y
My
2

>

“4
9)

S Ae,
ae
Ky)

N
»

l/
y

x
Y,

Y
ms
i

—

)

Ws

WW

\ WY
Vie
i)

RARE
~ <> ~~

LOS NS XZ

RAK ASSSS

SS BESS
Www rd SA SS SSN

and that at each extremity; while increase in thickness takes
place by the formation of layers of osseous tissue beneath
the periosteum. The former is an example of ossification
in cartilage; the latter of ossification in membrane.
Teeth.—A tooth is generally described as possessing a
crown, neck, and fang, or fangs. The crown is the portion
which projects beyond the level of the gum. The neck is
that constricted portion just below the crown which is

* Fig. 19. Lamelle torn off from a decalcified human parietal bone
at some depth from the surface. «, a lamella, showing reticular fibres ;
b, 6, darker part, where several lamellz are superposed ; ¢, ¢, perforating
fibres. Apertures through which perforating fibres had passed, are seen
especially in the lower part, a, a, of the figure. Magnitude as seen -
under a power of 200, but not drawn to a scale (from a drawing by :
Dr. Allen Thomson).

TEETH. 51

embraced by the free edges of the gum, and the fang
includes all below this.

On making a longitudinal section through the centre
of a tooth (figs. 20 and 21),
it is found to be princi-
pally composed of a hard
matter, dentine or ivory ;
while in the centre this (22%
dentine is hollowed out
into a cavity resembling in
general shape the outline
of the tooth, and called the
pulp-cavity, from its containing a very vascular and sensi-
tive little mass composed of connective tissue, blood-vessels
and nerves, which is called the tooth-pulp. The pulp is
continuous below, through an opening at the end of the
fang, with the mucous membrane of the gum. Capping
that part of the dentine which projects beyond the level
of the gum, is a layer of very hard calcareous matter, the
enamel, while sheathing the portion of dentine which is
beneath the level of the gum, is a layer of true bone, called
the cement or crusta petrosa. At the neck of the tooth the
cement is exceedingly thin, but it gradually becomes thicker
as it approaches and covers the lower end or apex of the
_ fang.

Dentine or ivory in chemical composition closely re-
sembles bone. It contains, however, rather less animal
matter; the proportion in 100 parts being about 28 of animal
matter to 72 of earthy. The former, like the animal matter
of bone, may be resolved into gelatin by boiling. The

4

* Fig. 20. Sections of an Incisor and Molar Tooth.—The longitudinal
sections show the whole of the pulp-cavity in the incisor and molar
teeth, its extension upwards within the crown, and its prolongation
downwards into the fangs, with the small aperture at the point of each :
these and the cross section show the relation of the dentine and enamel.

E 2

52 ELEMENTARY TISSUES.

earthy matter is made up chiefly of phosphate of lime,
with a small portion of the carbonate, and traces of some
other salts.

- Under the microscope, dentine is
seen to be finely channelled by a mul-
titude of fine tubes, which, by their
inner ends, communicate with the
pulp-cavity, and by their outer extre-
mities come into contact with the
under part of the enamel and cement,
and sometimes even penetrate them
for a greater or less distance. In
their course from the pulp-cavity to
the surface of the dentine, these mi-
nute tubes form gentle and nearly
parallel curves, and divide and sub-
divide dichotomously, but without
much lessening of their calibre until
they are approaching their peripheral
termination. From their sides proceed
other exceedingly minute secondary
canals, which extend into the dentine
between the tubules.

The tubules of the dentine, the
average diameter of which at their
inner and larger extremity is ,=);>, of an inch, contain fine
prolongations from the tooth-pulp which give the dentine
a certain faint sensitiveness under ordinary circumstances,
and, without doubt, have to do also with its nutrition.

BB
Za

Ul

¥?

ete
*

* Fig. 21. Magnified Longitudinal Section of a Bicuspid Tooth

(after Retzius)—1, the ivory or dentine, showing the direction and ~

primary curves of the dental tubuli; 2, the pulp-cavity, with the
small apertures of the tubuli into it ; 3, the cement or crusta petrosa,
covering the fang as high as the border of the enamel at the neck,
exhibiting lacune ; 4, the enamel resting on the dentine ; this has been
worn away by use from the upper part.

lied I Sp bene eal hingeys pad

a? te ee ee ee ee, eS ee ae ee

bee peytot aw RU

iw

4

TEETH. 53

The enamel, which is by far the hardest portion of a
tooth, is composed, chemically, of the same elements that
enter into the composition of dentine and bone. Its
animal matter, however, amounts only to about 2 or 3 per
cent.

Examined under the microscope, _ Fig. 22.* |
enamel is found composed of fine 7
hexagonal fibres (figs. 22 and 23),
which are set on end on the sur-
face of the dentine, and fit into
corresponding depressions in the
same. ‘They radiate in such a
manner from the dentine, that at
the top of the tooth they are more
or less vertical, while towards the
sides they tend to the horizontal
direction. Like the dentine-tu-
bules, they are not straight, but
disposed in wavy and parallel
curves. The fibres are marked by
transverse lines, and are mostly
solid, but some of them contain a MIG IA A
very minute canal. Te - yy, PRT

The enamel itself is coated on Gb; |
the outside by a very thin calcified WN) | Yi,

membrane, sometimes termed the : i ;
cuticle of the enamel.

The crusta petrosa, or cement, is composed of true bone,
and in it are lacune and canaliculi which sometimes
communicate with the outer finely-branched ends of the
dentine-tubules.

=

sh
SigqysSees
w asSte= >
Ratna

&

)

Sse

fh

* Fig. 22. Thin section of the enamel and a part of the dentine
{from K6lliker) *£2. a, cuticular pellicle of the enamel ; 0, enamel
fibres, or columns with fissures between them and cross strie ; ¢, larger
cavities in the enamel, communicating with the extremities of some of

the tubuli (¢).

54 ELEMENTARY TISSUES.

Development of T. veth.—The teeth are developed after the |

following manner :—Along the free edge of the tooth-
less gum in the foetus, there extends a groove, or small

¥G
70

trench, the primitive dental groove (Goodsir), and, from the
bottom of this, project ten small processes of mucous mem-
brane, or papille, containing blood-vessels and nerves. As
these papille grow up from below, the edges of the small
trench begin to grow in towards each other, and over-
shadow them, at the same time that each papilla is cut off
from its neighbour by the extension of a partition wall
from the gum, which grows in from each side to separate
the one from the other. Thus closed in above and all
around, each dental papilla is at length contained in a
separate sac, and gradually assumes the character of a
tooth by deposition on its surface of the various hard
matters which have been just enumerated as composing
the greater part of a tooth’s substance. The small vascular

* Fig. 23. Enamel fibres ( from Ko6lliker) **°. A, fragments and
single fibres of the enamel, isolated by the action of hydrochloric acid.
B, surface of a small fragment of enamel, showing the hexagonal ends
of the fibres.

;
¥
4)

*
ig

}

2 ae a ee

DEVELOPMENT OF TEETH. 55

papilla is gradually encroached upon and imprisoned by
the calcareous deposit, until only a small part of it is left
as the tooth-pulp, which remains shut up in the harder
substance, with only the before-mentioned small communi-
cation with the outside, through the end of the fang. In
this manner the first set of teeth,,or the milk-teeth, are
formed; and each tooth, by degrees developing, presses
at length on the wall of the sac enclosing it, and causing
its absorption, is cut, to use a familiar phrase.

The temporary or milk-teeth, having only a very limited
term of existence, gradually decay and are shed, while
the permanent teeth push their way from beneath, by
gradual increase and development, so as to succeed them.

The temporary teeth are ten in each jaw, namely, four
incisors, two canines, and four molars, and are replaced by ten
permanent teeth, each of which is developed from a small
sac set by, so to speak, from the sac of the temporary tooth
which precedes it, and called the cavity of reserve. The
number of the permanent teeth is, however, increased to
sixteen, by the development of three others on each side of
the jaw aftermuch the same fashion as that by which the
milk teeth were themselves formed. The beginning of
the development of the permanent teeth of course takes
place long before the cutting of those which they are to
succeed; one of the first acts of the newly-formed little
dental sac of a milk-tooth being to set aside a portion of
itself as the germ of its successor.

The following formula shows, at a glance, the com-
parative arrangement and number of the temporary and
permanent teeth :—

MO. CA. IN. CA. MO,
) Upper re es" fi'-o4 80
Temporary Teeth . = 20
Lower 2 4° 4k i

MO.BI. CA. IN. CA. BI. MO.
Upper 3 2 I 4 I 2 3=16

Permanent Teeth. 32

Lower 3 2 1t-.4° 1 12 3=16

56 | THE BLOOD.

From this formula it will be seen that the two bicuspid
teeth in the adult are the successors of the two molars in
thechild. They differ from them, however, in some
respects, the temporary molars having a stronger likeness
to the permanent than to their immediate descendants, the
so-called bicuspids. The temporary incisors and canines
differ but little, except in their smaller size, from their .
successors.

CHAPTER V.
THE BLOOD.

ALTHOUGH it may seem, in some respects, unadvisable to
describe the blood before entering upon the physiology of
those subservient processes which have for their end or
purpose its formation and development, yet there are
many reasons for taking such a course, and we may there-
fore at once proceed to consider the structural and chemical
composition of this fluid.

Wherever blood can be seen under a moderately high
microscope-power as it flows in the vessels of a living part,
it appears a colourless fluid containing minute coloured
particles. The greater part of these particles are red, when
seen en masse, and they are the source of the colour which,
so far as the naked eye can see, belongs to every part of the
blood alike. The colourless fluid is named liquor sanguinis ;
the particles are the blood corpuscles or blood-cells. The struc-
tural composition of the blood may be thus expressed :—

, Clot (containing also
Liquid Blood Corpuscles . * * / more or less serum).
rqure 21000" +) Liquor Sanguinis § Fibrin \
or Plasma. Serum
When blood flows from the living body, it is a thickish
heavy fluid, of a bright scarlet colour when it comes from

an artery ; deep purple, or nearly black, when it flows from

ODOUR OF BLOOD. 57

a vein. Its specific gravity at 60° F. is, on an average,
1055, that of water being reckoned as 1000; the extremes
consistent with health being 1050 and 1059. Its tempera-
ture is generally about 100° F.; but it is not the same in
all parts of the body. ‘Thus, while the stream is slightly
warmed by passing through the liver and some other parts,
itis slightly cooled, according to Bernard, by traversing
the capillaries of the skin. The temperature of blood in
the left side of the heart is, again 1° or 2° higher than in
the right (Savory).

The blood has a slight alkaline reaction; and emits an
odour similar to that which issues from the skin or breath
of the animal from which it flows, but fainter. The alka-
-line reaction appears to be a constant character of blood
in all animals and under all circumstances. An exception
has been supposed to exist in the case of menstrual blood ;
but the acid reaction which this sometimes presents is due
to the mixture of an acid mucus from the uterus and
vagina. Pure menstrual blood, such as may be obtained
with a speculum, or from the uteri of women who die
during menstruation, is always alkaline, and resembles
ordinary blood. According to Bernard, blood becomes
spontaneously acid after removal from the body, ORE to
conversion of its sugar into lactic acid.

The odour of blood is easily perceived in the watery
vapour, or hulitus as it is called, which rises from blood
just drawn; it may also be set free, long afterwards, by
adding to the blood a mixture of equal parts of sulphuric
acid and water. It is said to be not difficult to tell, by the
likeness of the odour to that of the body, the species of
domestic animal from which any specimen of blood has
been taken: the strong odour of the pig or cat, and the
peculiar milky smell of the cow, are especially easy to be
thus discerned in their blood (Barruel).

58 THE BLOOD.

Quantity of Blood.

Only an imperfect indication of the whole quantity of
blood in the body is afforded by measurement of that
which escapes, when an animal is rapidly bled to death,
inasmuch as a certain amount always remains in the blood-
vessels. In cases of less rapid bleeding, on the other
hand, when ‘life is more prolonged, and when, therefore,
sufficient time elapses before death to allow some absorp-
tion into the circulating current of the fluids of the body
(p. 84), the whole quantity of blood that escapes may be
greater than the whole average amount naturally present
in the vessels.

Various means have been devised, therefore, for obtain-
ing a more accurate estimate than that which results from
merely bleeding animals to death.

Welcker’s method is the following. An animal is.

rapidly bled to death, and the blood which escapes is col-
lected and measured, The blood remaining in the smaller
vessels is then removed by the injection of water through
them, and the mixture of blood and water thus obtained,
is also collected. The animal is then finely minced, and
infused in water, and the infusion is mixed with the com-
bined blood and water previously obtained. Some of this
fluid is then brushed on a white ground, and the colour
compared with that of mixtures of blood and water whose
proportions have been previously determined by measure-
ment. In this way the materials are obtained for a fairly
exact estimate of the quantity of blood actually existing in
the body of the animal experimented on.’

Another method (that of Vierordt) consists in estimating
the amount of blood expelled from the ventricle, at each
beat of the heart, and multiplying this quantity by the
number of beats necessary for completing the ‘round’ of
the circulation. This method is ingenious, but open to
various objections, the most conclusive being the uncer-

4
—
~
‘
j

QUANTITY OF BLOOD. 59

tainty of all the premisses on which the conclusion is
founded.

Other methods depend on the results of injecting a
known quantity of water (Valentin) or of saline matters
(Blake) into the blood-vessels; the calculation being
founded in the first case, on the diminution of the specific
gravity which ensues, and in the other, on the quantity of
the salt found diffused in acertain measured amount of
the blood abstracted for experiment.

A nearly correct estimate was probably made by Weber
and Lehmann, from the following data. A criminal was
weighed before and after decapitation; the difference in
the weight representing, of course, the quantity of blood
which escaped. The blood-vessels of the head and trunk,
were then washed out by the injection of water, until the
fluid which escaped had only a pale red or straw colour.
This fluid was then also weighed; and the amount of blood
which it represented was calculated, by comparing the
proportion of solid matter contained in it, with that of the
first blood which escaped on decapitation. Two experi-
ments of this kind gave precisely similar results.

The most reliable of these various means for estimating
the quantity of blood in the body yield as nearly similar
results as can be expected, when the sources of error un-
avoidably present in all, are taken into consideration; and
it may be stated that in man, the weight of the whole
quantity of blood, compared with that of the body, is from
about 1 to 8, to 1 to 10.

It must be remembered, however, that the whole quan-
tity of blood varies, even in the same animal, very consider-
ably, in correspondence with the different amounts of food
and drink, which may have been recently taken in, and
the equally varying quantity of matter given out. Bernard
found by experiment, that the quantity of blood obtainable
from a fasting animal is scarcely more than a half of that
which is present soon aftera full meal. The estimate above

60).> THE BLOOD

given, must therefore be taken to represent only an ap-
proximate average.

Coagulation of the Blood.

When blood is drawn from the body, and left at rest,
certain changes ensue, which constitute a kind of rough
analysis of it, and are instructive respecting the nature of
some of its constituents. After about ten minutes, taking
a general average of many observations, it gradually clots
or coagulates, becoming solid like a soft jelly. The clot
thus formed has at first the same volume and appearance
as the fluid blood had, and,-like it, looks quite uniform;
the only change seems to be, that the blood which was fluid
is now solid. But presently, drops of transparent yellowish
fluid begin to ooze from the surface of the solid clot; and
these gradually collecting, first on its upper surface, and
then all around it, the clot or “ crassamentum,” diminished
jn size, but firmer than it was before, floats in a quantity
of yellowish fluid, which is named serum, the quantity of
which may continually increase for from twenty-four to
forty-eight hours after the clotting of the blood.

7

The changes just described may be thus explained. The |

liquor sanguinis, or liquid part of the blood (p. 56), consists
of a thin fluid called serum, holding fibrin in solution.*
The peculiar property of fibrin, as already said, is its ten-
dency to become solid when at rest, and in some other
conditions. When, therefore, a quantity of blood is drawn
from the vessels, the fibrin coagulates, and the blood cor-
puscles, with part of the serum, are held, or, as it were,
entangled in the solid substance which it forms.

But after healthy fibrin has thus coagulated, it always

* This statement has been left unaltered in the text ; but, as will be
seen farther on, it requires modification.—(Ep.)

rm.

Depts ess eo NL ge cr 64 hos

> Ya

PY Bey 5 £3

COAGULATION OF BLOOD. > 61

contracts ; and what is generally described as one process
of coagulation should rather be regarded as consisting of
two parts or stages; namely, first, the simple act of clot-
ting, coagulating, or becoming solid; and, secondly, the
contraction or condensation of the solid clot thus formed,
By this second act much of the serum which was soaked
in the clot is gradually pressed out; and this collects in
the vessel around the contracted clot.

Thus, by the observation of blood within the vessels, and
of the changes which commonly ensue when it is drawn
from them, we may distinguish in it three principal consti-
tuents, namely, Ist, the fibrin, or coagulating substance ;
2nd, the serum; 3rd, the corpuscles.

That the fibrin is the only spontaneously coagulable
material in the blood, may be proved in many ways; and
most simply by employing any means whereby a portion
of the liquor sanguinis, z.¢., the serum and fibrin, can be
separated from the red corpuscles before coagulation.
Under ordinary circumstances coagulation occurs before
the red corpuscles have had time to subside; and thus,
from their beiny entangled in the meshes of the fibrin, the
clot is of a deep dark red colour throughout,—somewhat
darker, it may be, at the most dependent part, from accu-
» mulation of red cells, but not to any very marked degree.
If, however, from any cause, the red cells sink more
quickly than usual, or the fibrin contracts more slowly,
then, in either of these cases, the red corpuscles may be
observed, while the blood is yet fluid, to sink below its
surface; and the layer beneath which they have sunk, and
which has usually an opaline or greyish white tint, will
coagulate without them, and form a white clot consisting _
of fibrin alone, or of fibrin with entangled white cor-
puscles; for the white corpuscles, being very light, tend
upwards towards the surface of the fluid. The layer of
white clot which is thus formed rests on the top of a
coloured clot of ordinary character, i.c., of one in which

62 THE BLOOD.

the coagulating fibrin has entangled the red corpuscles
while they were sinking: and, thus placed, it constitutes
what has been called a buffy coat.

When a buffy coat is formed in the manner just de-
scribed, it commonly contracts more than the rest of the
clot does, and, drawing in at its sides, produces a cupped
appearance on the top of the clot. :

In certain conditions of the system, and especially when

there exists some local inflammation, this buffed and.

cupped condition of the clot is well marked, and there has
been much discussion concerning its origin under these
circumstances. It is now generally agreed that two causes
combine to produce it.

In the first place, the tendency of the red corpuscles to
form rouleaux: (see p. 73) is much exaggerated in inflam-
matory blood; and as their rate of sinking increases with
their aggregation, there is a ready explanation, at least in
part, of the colourless condition of the top of the clot.
And in the next place, inflammatory blood coagulates less
rapidly than usual, and thus there is more time for the
already rapidly sinking corpuscles to subside. ‘The colour-
_ less or buffed condition of the upper part of the clot is there-
fore, readily accounted far; while the cupped appearance is
easily explained by the greater power of contraction pos-
sessed by the fibrin of inflammatory blood, and by its
contraction being now not interfered with by the presence
of red corpuscles in its meshes.

Although the appearance just described is commonly
the result of a condition of the blood in which there is an
increase in the quantity of fibrin, it need not of necessity
be so. For a very different state of the blood, such as
that which exists in chlorosis, may give rise to the same
appearance; but in this case the pale layer is due to a
relatively smaller amount of ‘red corpuscles, not to any
increase in the quantity of fibrin.

It is thus evident that the coagulation of the blood is due

COAGULATION OF BLOOD. 63

to its fibrin. The cause of the coagulation of the fibrin,
however, is still a mystery.

The theory of Prof. Lister, that fibrin has no natural
tendency to clot, but that its coagulation out of the body
is due to the action of foreign matter with which it
happens to be brought into contact, and, in the body,
to conditions of the tissues, which cause them to act
towards it like foreign matter, is insufficient; because
even if it be true, it still leaves unexplained the manner
in which the fibrin, fluid in the living blood-vessels, can,
by foreign matter, be thus made solid. If it be
a fact, it is a very important one, but it is not an
explanation.

The same remark may be applied also to another theory
which differs from the last, in that while it admits a
natural tendency on the part of the blood to coagulation,
it supposes that this tendency in the living body is re-
strained by some inhibitory power resident in the walls of
_ the containing vessels. This also may, or may not, be
true; but it is only a statement of a possible fact, and
leaves unexplained the manner in which living tissue can
thus restrain coagulation.

Dr. Draper believes that coagulation takes place in the
living body, as out of it, or as in the dead; but in the one
case the fibrin is picked out in the course of the circu-
lation by tissues which this particular constituent of
the blood is destined to nourish; in the others, it remains
and becomes evident asa clot. This explanation is inge-
nious, but requires some kind of proof before it can be
adopted.

Concerning other theories, as for instance, that coagu-
lation is due to the escape of carbonic acid, or of ammonia,
it need only be said that they have been completely
disproved.

We must, therefore, for the edit believe that the
cause of the coagulation of the blood has yet to’ be dis-

64 THE BLOOD.

covered; but some very interesting observations in con-
nexion with the subject have been recently made, and seem
not unlikely to lead in time to a solution of this difficult
and most. vexed question. The observations referred to
have been made independently by Alexander Schmidt,
although he was forestalled in regard to some of his ex-
periments by Dr. Andrew Buchanan of Glasgow, many

_ years ago.

When blood-serum, or washed blood-clot, is added to
the fluid of hydrocele, or any other serous effusion, it
speedily causes coagulation, and the production of true
fibrin. And this phenomenon occurs also on the ad-

mixture of serous effusions from different parts of the

body, as that of hydrocele with that of ascites, or of either
with fluid from the cavity of the pleura. Other sub-
stances also, as muscular or nervous tissue, skin, etc.,
have been found also able to excite coagulation in serous
fluids. Thus, fluids which have little or no tendency to
coagulate when left to themselves, can be made, to produce.
a clot, apparently identical with the fibrin of blood by
the addition to them of matter which, on its part, was not
known to have any special relation to fibrin. As may be
supposed, the coagulation is not alike in extent under all
these circumstances. Thus, although it occurs when ap-

parently few or no blood-cells exist in either constituent of

the mixture, yet the addition of these very much increases
the effect, and their presence evidently has a very close
connexion with the process. From the action of the buffy
coat of a clot, in causing the appearance of fibrin in serous
effusions, it may be inferred that the pale as well as the
red corpuscles are influential in coagulation under these
circumstances. Blood-crystals are also found to be effec-
tive in producing a clot in serous fluids.

The true explanation of these very curious phenomena
is, probably, not fully known; but Schmidt supposes that
in the act of formation of fibrin there occurs the union

FORMATION OF FIBRIN. 65

of two substances, which he terms fibrino-plastin and
fibrinogen.

The substance which he terms fibrino-plastin, and which
he has obtained, not only from blood, but from many
other liquids and solids, as the crystalline lens, chyle and
lymph, connective tissue, etc., which are found capable of
exciting coagulation in serous fluids, is probably identical
with the globulin of the red corpuscles.

The fibrinogenous matter obtained from serous effusions
differs but little, chemically, from the fibrino-plastin.

Thus in the experiment before mentioned, the globulin
or fibrino-plastic matter of the blood-cells, in the clot,
causes coagulation by uniting with the fibrinogen present
in the hydrocele-fluid. And whenever there occurs coagu-
lation with the production of fibrin, whether in ordinary
blood-clotting, or in the admixture of serous effusions, or
in any other way, a like union of these two substances may
be supposed to occur. ©

The main result, therefore, of these very interesting
experiments and observations has been to make it probable
that the idea of fibrin existing in a liquid state in the
blood is founded on a mistaken notion of its real nature,
and that, probably, it does not exist at all in solution as
fibrin, but is formed at the moment of coagulation by
the union of two substances which, in fluid blood, exist
separately. bob

The theories before referred to, concerning the coagu-
lation of the blood, will therefore, if this be true, resolve
themselves into theories concerning the causes of the union
of fibrino-plastin and fibrinogen ; and whether, on the one
hand, itis an inhibitory action of the living blood-vessels
that naturally restrains, or a catalytic action of foreign
matter that excites, the union of these two substances.

66 =. (HE BLOOD.

Conditions affecting Coagulation.

Although the coagulation of fibrin appears to be spon-
taneous, yet it is liable to be modified by the conditions in
which it is placed ; such as temperature, motion, the access
of air, the substances with which it is in contact, the mode
of death, etc. All these conditions need to be considered
in the study of the coagulation of the blood.

The coagulation of the blood is hastened by the eapid
ing means :—

1. Moderate warmth,—from about 100° F. to 120° F.

2. Rest is favourable to the coagulation of blood. Blood,
of which the whole mass is kept in uniform motion, as
when a closed vessel completely filled with it is constantly
moved, coagulates very slowly and imperfectly. But rest.
is not essential to coagulation; for the coagulated fibrin
may be quickly obtained from blood by stirring it with
a bundle of small twigs;. and whenever any rough points
of earthy matter or foreign bodies are introduced into
the blood-vessels, the blood soon coagulates upon them.

3. Contact with foreign matter, and especially multi- |

plication of the points of contact. Thus, when all other
conditions are unfavourable, the blood will coagulate upon
rough bodies projecting into the vessels; as, for example,

- upon threads passed through arteries or aneurismal sacs,

or the heart’s valves roughened by inflammatory deposits
or calcareous accumulations. And, perhaps, this may
explain the quicker coagulation of blood after death in the
heart with walls made irregular by the fleshy columns,
than in the simple smooth-walled arteries and veins.

4. The free access of air.

5. Coagulation is quicker in shallow, than in tall and
narrow vessels.

6. The addition of less than twice the bulk of water.

The blood last drawn is said to coagulate more quickly
than that which is first let out.

CONDITIONS AFFECTING COAGULATION, 67

The coagulation of the blood is retarded by the following
means :—

1. Cold retards the coagulation of blood; and it is said
that, so long as blood is kept at a temperature below 40°
F., it will not coagulate at all. Freezing the blood, ‘of
course, prevents its coagulation; yet it will coagulate,
though not firmly, if thawed after being frozen; and it
will do so, even after it has been frozen for several months.
Coagulation is accelerated, but the subsequent contraction
of the clot is hindered, by a temperature between 100° and
120°: a higher temperature retards coagulation, or, by
coagulating the albumen of the serum, prevents if
altogether.

2. The addition of water in greater proportion than
twice the bulk of the blood.

3. Contact with living tissues, and especially with the
interior of a living blood-vessel, retards coagulation,
although if the blood be at rest it does not prevent it, .

4. The addition of the alkaline and earthy salts in the
proportion of 2 or 3 per cent. and upwards. ‘When added
in large proportion most of these saline substances pre-
vent coagulation altogether. Coagulation, however, en-
sues on dilution with water. The time that blood can be
thus preserved in a liquid state and coagulated by the
_ addition of water, is quite indefinite.

5. Imperfect aération,—as in the blood of those who die
by asphyxia.

6. In Inflammatory states of the system, the blood coa-
gulates more slowly although more firmly.

7. Coagulation is retarded by exclusion of the blood
from the air, as by pouring oil on the surface, etc. In
vacuo, the blood coagulates quickly; but Prof. Lister
thinks that the rapidity of the process is due to the bub-
bling which ensues from the escape of gas, and to the
blood being thus brought more freely into contact with the

containing vessel.
F 2

68 THE BLOOD.

The coagulation of the blood is prevented altogether by
the addition of strong acids and caustic alkalies.

It has been believed, and chiefly on the authority of Mr.
Hunter, that, after certain modes of death, the blood does
not coagulate; he enumerates the death by lightning,

over-exertion (as in animals hunted to death), blows on the ©

stomach, fits of anger. He says, ‘‘ I have seen instances
of them all.’”’ Doubtless he had done so; but the results
of such events are not constant. The blood has been often
observed coagulated in the bodies of animals killed by
lightning or an electric shock; and Mr. Gulliver has
published instances in which he found clots in the hearts
of hares and stags hunted to death, and of cocks killed in
fighting.

Chemical Composition of the Blood.

Among the many analyses of the blood that have been
published, some, in which all the constituents are enume-
rated, are inaccurate in their statements of the proportions
of those constituents; others, admirably accurate in some
particulars, are incomplete. The two following Tables,
constructed chiefly from the analyses of Denis, Lecanu,
Simon, Nasse, Lehmann, Becquerel, Rodier, and Gavarret,
are designed to combine, as far as possible, the advan-
tage of accuracy in numbers with the convenience of
presenting at one yiew, a list of all the constituents of the
blood.

Average proportions of the principal constituents of the
blood in 1,000 parts :—

Water . : : ; , ‘ = - Nae 5
Red corpuscles (solid residue) . ; : ag et See
Albumen of serum . ; : ; : ; eats tx
Saline matters . : ‘ ; : s eae 6°03
Extractive, fatty, and other matters : 3 : 7°77
Fibrin ; : . ‘ ; : i eth 22
1C00*

=. fio

we were

COMPOSITION OF BLOOD. 69

Average proportions of all the constituents of the blood
in 1,000 parts :—

Water . F : / ; ; ‘ ; er ae
Albumen. . ; ‘ , : i ies 70°
Fibrin : ae : , . . . 2°2
Red corpuscles (dry). ° ; : é ‘7 Es6!
_ Fatty matters . steer . . I°4
‘Inorganic salts: Cliloride of sodium . ; ; 3°6
Chloride of potassium . ee 0°35
Tribasic phosphate of soda . : o'2
Carbonate of soda . i Gh. 0°28
Sulphate of soda . : : ‘ 0°28
Phosphates of lime and magnesia. 0°25
Oxide and phosphate of iron , O°5
Extractive matters, biliary colouring matter, gases,
and accidental substances : ; : E 6°40
1000°
Elementary composition of the dried blood of the ox :—
Carbon ‘ . 2 ‘ ‘ ; ; s 57°9
Hydrogen ; : ‘ ; ‘ ; mah ped
Nitrogen ., : ' : ‘ ; ; Pay y hy
Oxygen .. 4 - P : Bs be i i 2 iO!
Ashes . ‘ ‘ ; ‘ : : j . ae

These results of the ultimate analysis of ox’s blood afford
a remarkable illustration of its general purpose, as supply-
ing the materials for the renovation of all the tissues. For
the analysts (Playfair and Boeckmann) have found that
the flesh of the ox yields the same elements in so nearly
the same proportions, that the elementary composition of
the organic constituents of the blood and flesh may be con-
sidered identical, and may be represented for both by the
formula C,;H..N,0,;.

The Blood-Corpuscles or Blood-Cells.'

It has been already said, that the clot of blood contains,
with the fibrin and the portion of the serum that is soaked
in it, the blood-corpuscles, or blood-cells. Of these there are

70 THE BLOOD.

two principal forms, the red and the white corpuscles.

When coagulation has taken place quickly, both kinds of
Fig. 24.*

Mammals. Birds. Reptiles. Amphibia. Fish.

tl i i a

OSTRICH

CROCODILE

K DEEF
8

MUSK D

PIGEON
ELECTRIC EEL..

PROTEUS

-
2
<
0
<
wW
p x
a

TRITON

LIZARD

HUMMING BIRD

* The above illustration is somewhat altered from a drawing, by Mr.
Gulliver, in the Proced. Zool. Society, and exhibits the typical characters
of the red-blood cells in the main divisions of the Vertebrata. The
fractions are those of an inch, and represent the average diameter. In

RED BLOOD-CORPUSCLES. v5:

corpuscles may be uniformly diffused through the clot;
but, when it has been slow, the red corpuscles, being the
heaviest constituent of the blood, tend by gravitation to
accumulate at the bottom of the clot; and the white cor-
puscles, being among the lightest constituents, collect in
the upper part, and contribute to the formation of the
buffy coat.

The human red blood-cells or blood corpuscles (figs. 25 and
29) are circular flattened disks of different sizes, the majority
varying in diameter from +}, to <5/5> of an inch, and about
sotss of an inch in thickness. When viewed singly, they
appear of a pale yellowish tinge ; the deep red colour which
they give to the blood being observable in them only when
they are seen en masse. Their borders are rounded; their
surfaces, in the perfect and most usual state, slightly con-
caye; but they readily acquire flat or convex surfaces
when, the liquor sanguinis being diluted, they are swollen
by absorption of fluid. They are composed of a colourless,
structureless, and transparent filmy framework or stroma
infiltrated in all parts by a red colouring-matter termed
hemoglobin. « The stroma is tough and elastic, so that, as
the cells circulate, they admit of elongation and other
changes of form, in adaptation to the vessels, yet recover
their natural shape as soon as they escape from compres-
sion. The term cell, in the sense of a bag or sac, is inap-
plicable to the red blood-corpuscle; and it must be con-

the case of the oval cells, only the long diameter is here given. It is
remarkable, that although the size of the red blood-cells varies 80 much
in the different classes of the vertebrate kingdom, that of the white
corpuscles remains comparatively uniform, and thus they are, in some
animals, much greater, in others much less than the red corpuscles
existing side by side with them.

It may be here remarked, that the appearance of a nucleus in the red
blood-cells of birds, reptiles, amphibia and fish has been shown by Mr.
Savory to be the result of post-mortem change ; no nucleus being
visible in the cells as they circulate in the living body, or in those
which have just escaped from the blood-vessels.

72 THE BLOOD.

sidered, if not solid throughout, yet as having no such
variety of consistence in different parts as to justify the
notion of its being a membranous sac with fluid contents. —
The stroma exists in all parts of its substance, and the
colouring-matter uniformly pervades this, and is not merely
surrounded by and mechanically enclosed within the outer
wall of the corpuscle. The red corpuscles have no nuclei,
although, in their usual state, the unequal refraction of
transmitted light gives the appearance of a central spot,
brighter or darker than the border, according as it is
viewed in or out of focus. Their specific gravity is about
1088.

In examining a number of red corpuscles with a micro-
scope, it is easy to observe certain natural diversities among
them, though they may have been all taken from the same
part. The great majority, indeed, are very uniform; but
some are rather larger, and the larger ones generally
appear paler and less exactly circular than the rest; their
surfaces also are, usually, flat or slightly convex, they often
contain a minute shining particle like a nucleolus, and they
are lighter than the rest, floating higher in the fluid in
which they are placed. Other deviations from the general
characters assigned to the corpuscles, depend on changes
that occur after they are taken from the body. Very com-
monly they assume a granulated or mulberry-like form, in
consequence, apparently, of a peculiar corrugation of their
cell-walls. Sometimes, from the same cause, they present
a very irregular, jagged, indented, or star-like appearance.
The larger cells are much less liable to this change than
the smaller, and the natural shape may be restored by
diluting the fluid in which the corpuscles float; by such
dilution the corpuscles, as already said, may be made to
swell up, by absorbing the fluid; and, if much water be
added, they will become spherical and pellucid, their
colouring-matter being dissolved, and, as it were, washed .
out of them. Some of them may thus be burst; the others

RED BLOOD-CORPUSCLES. 73

are made obscure ; but many of these latter may be brought
into view again by evaporating, or adding saline matter to,
the fluid, so as to restore it to its previous density. The -
changes thus produced by water are more quickly effected
by weak acetic acid, which immediately makes the cor-
puscles pellucid, but dissolves few or none of them, for

7 _ the addition of an alkali, so as to neutralise the acid, will

restore their form though not their colour.

A peculiar property of the red corpuscles, which is exag-
gerated in inflammatory blood, and which appears to exist
in a marked degree in the blood of horses, may be here
noticed. It gives them a great tendency to adhere together
in rolls or columns, like piles of coins, and then, very
quickly, these rolls fasten together by their ends, and
cluster; so that, when the blood is spread out thinly on a
glass, they form a kind of irregular network, with crowds
of corpuscles at the several points corresponding with the
knots of the net (fig. 25). Hence,
the clot formed in such a thin
layer of blood looks mottled
with blotches*of pink upon a
white ground : in a larger quan-
tity of such blood, as soon as
the corpuscles have clustered
and collected in rolls (that is,
generally in two or three minutes _
after the blood is drawn), they
begin to sink very quickly; for in the aggregate they pre-
sent less surface to the resistance of the liquor sanguinis
than they would if sinking separately. Thus, quickly sink-
ing, they leave above them a layer of liquor sanguinis,
and this coagulating, forms a buffy coat, as before de-
scribed, the volume of which is augmented by the white
corpuscles, which have no tendency to adhere to the red
ones, and by their lightness float up clear of them.

* Fig. 25. Red corpuscles collected into rolls (after Henle).

74 THE BLOOD.

Chemical Composition of Red Blood-cells.

It has been before remarked that the red blood-corpuscles
are formed of a colourless stroma, infiltrated with a colour-
ing matter termed hemoglobin. As they exist in the
blood they contain about three-fourths of their weight of
water.

The stroma appears to be composed of a nitrogenous
proximate principle termed protagon, combined with albu-
minous matter (paraglobulin. or fibrinoplastin), fatty mat-
ters including cholesterin, and salts, chiefly phosphates, of
potash, soda and lime.

Heemoglobin, which enters far more largely into the com-
position of the red corpuscles than any other of their con-
stituents, is allied to albumen in some respects, but differs
remarkably from it in others. One of its most marked

distinctive characters is its tendency under certain arti-.

ficial conditions to crystallize; the so-called blood-crys-
tals being but the natural so hae ai forms assumed by
this substance.

Heemoglobin can be obtained in a crystalline form with
various degrees of difficulty from the blood of different
animals, that of man holding an intermediate place in this
respect. Among the animals whose blood colouring-matter
crystallizes most readily, are the guinea-pig and the dog ;
and in these cases to obtain crystals it is generally suffi-
cient to dilute a drop of recently drawn blood with water
and expose it for a few minutes to the air. In many
instances, however, a somewhat less simple process must be
adopted; as theaddition of chloroform or ether, rapid freezing
and then thawing, or other means which separate the colour-
ing-matter from the other constituents of the corpuscles.

Different forms of blood-crystals are shown in the accom-
panying figures,

Another and most important character of heemoglobin is
its attraction for oxygen, and some other gases, as carbonic

ot had a ee

BLOOD-CRYSTALS. 75

and nitrous oxides, with all of which it appears to form ~
definite chemical combinations. The combination with
oxygen is that which
is of most physio-
logical importance.
During the passage
of the blood through
the lungs, it is con-
stantly formed; while
it is as constantly
decomposed, in con-
sequence of the rea-
diness with which
hemoglobin _ parts
with oxygen, when
the latter is exposed
to other attractions
in its circulation
through the — sys-
temic capillaries.
Thus, the red cor-
puscles, in virtue of
their colouring mat-
ter, which readily
absorbs oxygen and
as readily gives it
up again, are the
chief means by which
oxygen is carried in
the blood (see also

p. 85).

Fig. 26." ~.

* Figs. 26, 27, and 28, illustrate some of the principal forms of
blood-erystals :-—

Fig. 26, Prismatic, from human blood.

+ Fig. 27, Tetrahedral, from blood of the guinea-pig.

76 THE BLOOD.

By heat, mineral and other acids, alkalies, etc., hamo-

Fig. 28.* globin is decomposed
into an albuminous
matter (resembling
globulin) and hema-
tin. The latter, now
known to be a pro-
duct of the decom-
position of hzemo-
globin, was once
thought to be the
natural _ colouring
matter of the blood.

The White Corpuscles of the Blood or Blood Leucocytes.

The white corpuscles are much less numerous than the
red. Onan average, in health, there may be’one white
to 400 or 500 red corpuscles ; but in disease, the propor-
tion is often as high as one to ten, and sometimes even
much higher.

In health, the proportion varies considerably even in
the course of the same day. The variations appear to

depend chiefly on the amount and probably also on the -

kind of food taken; the number of leucocytes being very
considerably increased by a meal, and diminished again on
fasting.

They present greater diversities of form than the red

ones do; but the gradations between the extreme forms
are so regular, that no sufficient reason can be found for

supposing that there is in healthy blood more than one

species of white corpuscles. In their most general appear-

* Fig. 28. Hexagonal crystals from blood of squirrel. On these
six-sided plates, prismatic crystals, grouped in a stellate manner, not
unfrequently occur (after Funke).

ee

;
a Te

WHITE BLOOD-CORPUSCLES. 77

ance, they are circular and nearly spherical, about 5.1, of
an inch in diameter (fig. 29). ‘They have a greyish,
pearly look, appearing variously shaded or nebulous, the
shading being much darker in some than in others. They
seem to be formed of Reopen (p. 19), containing
granules which are in

some specimens few and Fig. 29.*

very distinct, in others
(though rarely) so nu-
merous that the whole
corpuscle looks like a
mass of granules.

These corpuscles can-
not be said to have any
true cell-wall. Ina few
instances an apparent
cell-membrane can be
traced around them;
but, much more commonly, even this is not discernible till
after the addition of water or dilute acetic acid, which
penetrates the* corpuscle, and lifts up and distends what
looks like a cell-wall, to the interior of which the mate-
rial, that before appeared to form the whole corpuscle,
remains attached as the nucleus of the cell (fig. 29).

A remarkable property of the white corpuscles, first
observed by Mr. Wharton Jones, consists in their capa-
bility of assuming different forms, irrespective of any
external influence. If a drop of blood be examined
with a high microscope power under conditions by which
loss of moisture is prevented, at the same time that the
temperature is maintained at about the degree natural to
‘the blood as it circulates in the living body, the leu-

* Fig. 29. Red and white blood-corpuscles. a, White corpuscle of
natural aspect. 6, Three white corpuscles acted on by weak acetic acid.
¢, Red blood corpuscles.

78 THE BLOOD. . y

cocytes can be seen alternately contracting and dilating

very slowly at various parts of their circumference,—shoot-
ing out irregular processes, and again withdrawing them
partially or completely, and thus in succession assuming
various irregular forms.

These movements, called ameboid, from their resem-
blance to the movements exhibited by an animal called
the Ameba, the structure of which is as simple as that of
a white blood-corpuscle, are characteristic of the living
leucocyte, and form a good example of the contractile pro-
perty of protoplasm, before referred to. Indeed, the unchang-
ing rounded form which the corpuscles present in specimens
of blood examined in the ordinary manner under the micro-
scope, must be looked upon as the shape natural to a
dead corpuscle, or one whose vitality is dormant, rather
than as the proper shape of one living and active.

Besides the red and white corpuscles, the microscope
reveals numerous minute molecules or granules in the blood,
circular or spherical, and varying in size from the most
minute visible speck to the =, of an inch (Gulliver).
These molecules are very similar to those found in the
lymph and chyle, and are, some of them, fatty, being
soluble in ether, others probably albuminous, being soluble
in acetic acid. Generally, also, there may be detected in
the blood, especially during the height of digestion, very
minute equal-sized fatty particles, similar to those of which
the molecular base of chyle is constituted (Gulliver). |

The Serum.

The serum is the liquid part of the blood remaining after
the coagulation of the fibrin. In the usual mode of
coagulation, part of the serum remains soaked in the clot,
and the rest, squeezed from the clot by its contraction, lies
around and over it. The quantity of serum that appears
around the clot depends partly on the total quantity in the
blood, but partly also on the degree to which the clot con-

ee

sre”? S wet

ah

lant iain:

i
n

SERUM OF BLOOD. 79

tracts. This is affected by many circumstances : generally,
the faster the coagulation the less is the amount of con-
traction ; and, therefore, when blood coagulates quickly, it
will appear to contain a small proportion of serum. Hence,
theserum always appears deficient in blood drawn slowly into
a shallow vessel, abundant in inflammatory blood drawn into
a tall vessel. In all cases, too, it should be remembered, that,
since the contraction of the clot may continue for thirty-six

_ or more hours, the quantity of serum in the blood cannot

be even roughly estimated till this period has elapsed.

The serum is an alkaline, slimy or viscid, yellowish fluid,
often presenting a slight greenish, or greyish hue, and with
a specific gravity of from 1025 to 1030. It is composed of
a mixture of various substances dissolved in about nine
times their weight of water. It contains, indeed, the
greater part of all the substances enumerated as existing
in the blood, with the exception of the fibrin and the red
corpuscles. Its principal constituent is albumen, of which
it contains about 8 per cent., and the coagulation of which,
when heated, converts nearly the whole of the serum into
a solid mass. «Ihe liquid which remains uncoagulated,
and which is often enclosed in little cavities in the coagu-
lated serum, is called serosity: it contains, dissolved in
water, fatty, extractive, and saline matters.

Variations in the principal Constituents of the Liquor Sanguinis.

The water of the blood is subject to hourly variations in its
quantity, according to the period since the taking of food,
the amount of bodily exercise, the state of the atmosphere,
and all the other events that may affect either the ingestion
or the excretion of fluids. According to these conditions,
it may vary from 700 to 790 parts in the thousand. Yet
uniformity is on the whole maintained; because nearly
all those things which tend to lower the proportion of water
in the blood, such as active exercise, or the addition of
saline and other solid matter, excite thirst; while, on the

Ba": THE BLOOD.

other hand, the addition of an excess of water to the blood
is quickly followed by its more copious excretion in sweat
and urine. And these means for adjusting the proportion
of the water find their purpose in maintaining certain im-
portant physical conditions in the blood; such as its proper
viscidity, and the degree of its adhesion to the vessels
through which it ought to flow with the least possible
resistance from friction. On this also depends, in great
measure, the activity of absorption by the blood-vessels,
into which no fluids will quickly penetrate, but such as are
of less density than the blood. Again, the quantity of
water in the blood determines chiefly its volume, and
thereby the fulness and tension of the vessels and the
quantity of fluid that will exude from them to keep the
tissues moist. Finally, the water is the general solvent of
all the other materials of the liquor sanguinis.

It is remarkable, that the proportion of water in the
blood may be sometimes increased even during its abstrac-
tion from an artery or vein. Thus Dr. Zimmerman in
bleeding dogs, found the last drawn portion of blood
contain 12 or 13 parts more of water in 1000 than the
blood first drawn; and Polli noticed a corresponding
diminution in the specific gravity of the human blood
during venesection, and suggested the only probable ex-
planation of the fact, namely, that during bleeding, the
blood-vessels absorb very quickly a part of the serous
fluid with which all the tissues are moistened. |

The albumen may vary, consistently with health, from 60
to 70 parts in the 1000 of blood. The form in which it
exists in the blood is not yet certain. It may be that of
simple solution as pure albumen: but it is, more probably,
in combination with soda, as an albuminate of soda; for,
if serum be much diluted with water, and then neutralized
with acetic acid, pure albumen is deposited. Another
view entertained by Enderlin is that the albumen is dis-
solved in the solution of the neutral phosphate of sodium,

FATTY MATTERS IN THE BLOOD. 8I

to which he considers the alkaline reaction of the blood to
be due, and solutions of which can dissolve large quantities
of albumen and phosphate of lime.

The proportion of jibrin in healthy blood may vary be-
tween 2 and 3 parts in 1000. In some diseases, such as
typhus, and others of low type, it may be as little as 1:034;
in other diseases, it is said, it may be increased to as much
as 7°528 parts in 1000. But, in estimating the quantity
of fibrin, chemists have not taken account of the white
corpuscles of the blood. These cannot, by any mode of
analysis yet invented, be separated from the fibrin of
mammalian blood: their composition is unknown, but
their weight is always included in the estimate of the
fibrin. In health, they may, perhaps, add too little to its
weight to merit consideration, but in many diseases, espe-
cially in inflammatory and other blood diseases in which
the fibrin is said to be increased, these corpuscles become
so numerous that a large proportion of the supposed
increase of the fibrin must be due to their being weighed
with it. On this account all the statements respecting the
increase of fibrin in certain diseases need revision.

The enumeration of the fatty matters of the blood makes
it probable that most of those which are found in the
tissues or secretions exist also ready-formed in the blood ;
for it contains the cholesterin of the bile, the cerebrin
and phosphorised fat of the brain, and the ordinary saponi-
fiable fats, stearin, olein, and palmatin. A volatile fatty
acid is that on which the odour of the blood mainly de-
pends; and it is supposed that when sulphuric acid is
added (see p. 57), it evolves the odour by combining
with the base with which, naturally, this acid is neutra-
lized. According to Lehmann, much of the fatty matter of
the blood is accumulated in the red corpuscles.

These fatty matters are subject to much variation in
quantity, being commonly increased after every meal in

which fat, or starch, or saccharine substances have been
: G

82 THE BLOOD.

taken. At such times, the fatty particles of the chyle,
added quickly to the blood, are only gradually assimilated ;
and their quantity may be sufficient to make the serum of
the blood opaque, or even milk-like.

As regards the inorganic constituents of the blood,—the
substances which remain as ushes after its complete burning
_—one may observe in general their small quantity in pro-
portion to that of the animal matter contained in it.

Those among them of peculiar interest are the phosphate
and carbonate of sodium, and the phosphate of calcium.

It appears most probable, that the blood owes its alkaline
reaction to both these salts of sodium. The existence of the
neutral phosphate (Na,H.PO,) was proved by Enderlin :
the presence of carbonate of sodium has been proved by
Lehmann and others. )

In illustration of the characters which the blood may
derive from the phosphate of sodium, Liebig points out the
_ large capacity which solutions of that salt have of absorb-
ing carbonic acid gas, and then very readily giving it off

again when agitated in atmospheric air, and when the

atmospheric pressure is diminished. It is probably, also,
by means of this salt, that the phosphate of calcium is held
in solution in the blood in a form in which it is not soluble
in water, or in a solution of albumen. Of the remaining
inorganic constituents of the blood, the oxide and phos-
phate of iron referred to, exist in the liquor sanguinis,
independently of the iron in the corpuscles.

Schmidt’s investigations have shown that the inorganic
constituents of the blood-cells somewhat differ from those
contained in the serum; the former possessing a consider-
able preponderance of phosphates and of the salts of potas-
sium, while the chlorides, especially of sodium, with phos-
phate of sodium, are particularly abundant in the latter.

Among the extractive matters of the blood, the most
noteworthy are Creatin and Creatinin. Besides these,
other organic principles have been found either constantly

-_ 7 ~ =

tt Peet

VARIATIONS OF BLOOD. 83

or generally in the blood, including casein, especially in
women during lactation: glucose, or grape-sugar, found in
the blood of the hepatic vein, but disappearing during its
transit through the lungs (Bernard); urea, and-in very
minute quantities, wric acid (Garrod) ; hippurie and lactic
acids ; ammonia (Richardson); and lastly, certain colouring
and odoriferous matters.

Variations in healthy Blood under different Circumstances.

As the general condition of the body depends so much
on the condition of the blood, and as, on the other hand,
anything that affects the body must sooner or later, and
. to a greater or less degree, affect the blood also, it might
be expected that considerable variations in the qualities of
this fluid would be found under different circumstances of
disease ; and such is found to be the case. Even in health,
however, the general composition of the blood varies con-
siderably. |

The conditions which appear most to influence the com-
position of the blood in health, are these: sex, pregnancy,
age, and temperament. The composition of the blood is

also, of course, much influenced by diet.
1. Sex.—The blood of men differs from that of women,

chiefly in being of somewhat higher specific gravity, from its
containing a relatively larger quantity of red corpuscles.

2. Pregnancy.—The blood of pregnant women has a
rather lower specific gravity than the average, from de-
ficiency of red corpuscles. The quantity of white corpuscles,
on the other hand, and of fibrin, is increased.

3. Age.—From the analysis of Denis it appears that the
blood of the foetus is very rich in solid matter, and espe-
cially in red corpuscles; and this condition, gradually
diminishing, continues for some weeks after birth. The
quantity of solid matter then falls during childhood below
the average, again rises during adult life, and in old age

falls again.
G2

84 THE BLOOD.

4. Temperament.—But little more is known concerning
the connection of this with the condition of the blood, than
that there appears to be a relatively larger quantity of solid
matter, and particularly of red corpuscles, in those of a
plethoric or sanguineous temperament.

5. Diet.—Such differences in the composition of the
blood as are due to the temporary presence of various
matters absorbed with the food and drink, as well as the
more lasting changes which must result from generous or
poor diet respectively, need be here only referred to.

Effects of Bleeding.—The result of bleeding is to diminish
the specific gravity of the blood; and so quickly, that in a
single venesection, the portion of blood last drawn has often
a less specific gravity than that of the blood that flowed
first (J. Davy and Polli). This is, of course, due to ab-
sorption of fluid from the tissues of the body. The physio-
logical import of this fact, namely, the instant absorption
of liquid from the tissues, is the same as that of the intense
thirst which is so common after either loss of blood, or the
abstraction from it of watery fluid, as in cholera, diabetes,
and the like. |

For some little time after bleeding, the want of red

-blood-cells is well marked; but, with this exception, no
considerable alteration seems to be produced in the com-
position of the blood for more than a very short time, the
loss of the other constituents, including the pale corpuscles,
being very quickly repaired.

Variations in the Composition of the Blood, in different Parts.

of the Body.

The composition of the blood, as might be expected, is
found to vary in different parts of the body. Thus arterial
blood differs from venous; and although its composition
and general characters are uniform throughout the whole
course of the systemic arteries, they are not so throughout

:
7
:
y

VARIATIONS OF BLOOD. 85

the venous system,—the blood contained in some veins
differing remarkably from that in others.

1. Differences between arterial and venous blood.—These
may be arranged under two heads,—differences in colour,
and in general composition.

a. Colour.—Concerning the cause of the difference in
colour between arterial and venous blood, there has been
much doubt, not to say confusion. For while the scarlet
colour of the arterial blood has been supposed by some
observers, and for some reasons, to be due to the chemical
action of oxygen, and the purple tint of that in the veins
to the action of carbonic acid, there are. facts which made
it seem probable that the cause was a mechanical one
rather than a chemical, and that it depended on a difference
in the shape of the red corpuscles, by which their power of
transmitting and reflecting light was altered. Thus, car-
bonie acid was thought to make the blood dark by causing
the red cells to assume a bi-convex outline, and oxygen
was supposed to reverse the effect by contracting them and
rendering them bi-concave. We may believe, however,
that, at least ‘for the present, this vexed question has, by
the results of investigations undertaken by Professor Stokes
and others, been now set at rest.

The colouring matter of the blood, or heemoglobin (p. 74),
is capable of existing in two different states of oxidation,
and the respective colours of arterial and venous blood are
caused by differences in tint between these two varieties—
oxidised or scarlet hemoglobin and de-oxidised or purple
hemoglobin... The change of colour produced by the passage
‘of the blood through the lungs, and its consequent exposure
to oxygen, is due, probably, to the oxidation of purple,
and its conversion into scarlet hemoglobin; while the
readiness with which the latter is de-oxidised offers a
reasonable explanation of the change, in regard to tint, of

arterial into venous blood, —the transformation being
effected by the delivering up of oxygen to the tissues, by

86 THE BLOOD.

the scarlet hemoglobin, during the blood’s passage through
the capillaries. The changes of colour are more probably
due to this cause, namely, a varying quantity of oxygen
chemically combined with the hemoglobin, than to any
mechanical effect of this gas, or to the influence of carbonic
acid, either chemically, on the colouring matter, or me-
chanically, on the corpuscles which contain it. We are
not, perhaps, in a position to deny altogether the possible
influence of mechanical conditions of the red corpuscles on
the colour of arterial and venous blood respectively ; but it
is probable that this cause alone would be quite insufficient
to explain the differences in the colour of the two kinds of
blood, and therefore if it be an element at all in the change,
it must be allowed to take only a subordinate position.

The distinction between the two kinds of hemoglobin
naturally present in the blood, or, in other words, the
proof that the addition or subtraction of oxygen involves
the production respectively of two substances having funda-
mental differences of chemical constitution, has been made
out chiefly by spectrum-analysis,—the effects produced by
placing oxidised and de-oxidised solutions of heemoglobin
in the path of a ray of light traversing a spectroscope being
different. For while théoxidised solution causes the ap-
pearance of two absorption bands in the yellow and the
green part of the spectrum, these are replaced by.a single band
intermediate in position, when the oxidised or scarlet solution
is darkened by de-oxidising agencies,—or, in other words,
when the change which naturally ensues in the ‘conversion
of arterial into venous blood is artificially produced.*

The greater part of the hemoglobin in both arterial and
venous blood probably exists in the scarlet or more highly
oxidised condition, and only a small part is de-oxidised and
made purple in its passage from the arteries into the veins.

* The student to whom the terms employed in connection with
spectrum analysis are not familiar, is advised to consult, with reference
to the preceding paragraph, an elementary treatise on Physics.

=

BLOOD OF PORTAL VEIN. 87

A 4

The differences in regard to colour between arterial and
venous blood are sometimes not to be observed. If blood
runs very slowly from an artery, as from the bottom of a
deep and devious wound, it is often as dark as venous
blood. “In persons nearly asphyxiated also, and some-
times, under the influence of chloroform or ether, the
arterial blood becomes like the venous. In the fcetus
also both kinds of blood are dark. But, in all these cases,
the dark blood becomes bright on exposure to the air.
Bernard has shown that venous blood returning from a gland
in active secretion is almost as bright as arterial blood.

b. General Composition.—The chief differences between
arterial and ordinary venous blood are these. Arterial
blood contains rather more fibrin, and rather less albumen
and fat. It coagulates somewhat more quickly. Also, it
contains more oxygen, and less carbonic acid. According
to Denis, the fibrin of venous blood differs from arterial,
in that when it is fresh, and has not been much exposed
to the air, it may be dissolved in a slightly heated solution
of nitrate of potassium.

Some of the veins, however, contain blood which differs
from the ordinary standard considerably. These are the

portal, the hepatic, and the splenic veins.

Portal vein.—The blood which the portal vein conveys
to the liver is supplied from two chief sources; namely,
that in the gastric and mesenteric veins, which contains
the soluble elements of food absorbed from the stomach
and intestines during digestion, and that in the splenic
vein; it must, therefore, combine the qualities of the
blood from each of these sources.

The blood in the gastric and mesenteric veins will vary
much according to the stage of digestion and the nature
of the food taken, and can therefore be seldom exactly the
same. Speaking generally, and without considering the
sugar, dextrine, and other soluble matters which may
have been absorbed from the alimentary canal, this blood |

88 THE BLOOD,

appears to be deficient in solid matters, especially in red
corpuscles, owing to dilution by the quantity of water ab-
sorbed, to contain an excess of albumen, though chiefly of
a lower kind than usual, resulting from the digestion of ni-
trogenised substances, and termed albuminose, and to yield
a less tenacious kind of fibrin than that of blood generally.

The blood from the splenic.vein is probably more definite
in composition, though also liable to alterations according
to the stage of the digestive process, and other circum-
stances. It seems generally to be deficient in red cor-
puscles, and to contain an unusually large proportion of
albumen. The fibrin seems to vary in relative amount,
but to be almost always above the average. The propor-
tion of colourless corpuscles appears also to be unusually
large. The whole quantity of solid matter is decreased,
the diminution appearing to be chiefly in the proportion
of red corpuscles.

The blood of the portal vein, combining the peculiarities
of its two factors, the splenic and mesenteric venous
blood, is usually of lower specific gravity than blood
generally, is more watery, contains fewer red corpuscles,
more albumen, chiefly in the form of albuminose, and
yields a less firm clot than that yielded by other blood,
owing to the deficient tenacity of its fibrin. These
characteristics of portal blood refer to the composition of
the blood itself, and have no reference to the extraneous
substances, such as the absorbed materials of the food,
which it may contain; neither, indeed, has any complete
analysis of these been given.

Comparative analyses of blood in the portal vein and
blood in the hepatic veins have also been frequently made,
with the view of determining the changes which this fluid
undergoes in its transit through the liver. Great diversity,
however, is observable in the analyses of these two kinds
of blood by different chemists. Part of this diversity is no
doubt attributable to the fact pointed out by Bernard, that

GASES OF THE BLOOD. 89

unless the portal vein is tied before the liver is removed
from the body, hepatic venous blood is very liable to
regurgitate into the portal vein, and thus vitiate the result
of the analysis. Guarding against this source of error,
recent observers seemed to have determined that hepatic
venous blood contains less water, albumen, and salts, than
the blood of the portal vein; but that it yields a much
larger amount of extractive matter, in which, according to
Bernard and others, is one constant element, namely, grape-
sugar, which is found, whether saccharine or farinaceous
matter have been present in the food cr not. |

Besides the rather wide difference between the composi-
tion of the blood of these veins and of others, it must not be
forgotten that in its passage through every organ and tissue
of the body, the blood’s composition must be varying con-
stantly, as each part takes from it or adds to it such matter
as it, roughly speaking, wishes either to have or to throw
away. Thus the blood of the renal vein has been proved
by experiment to contain less water than does the blood of
the artery, and doubtless its salts are diminished also. The
blood in the renal vein is said, moreover, by Bernard and
Brown-Séquard not to coagulate.

This then is an example of the change produced in the
blood by its passage through a special excretory organ. But
all parts of the body, bones, muscles, nerves, etc., must act
on the blood as it passes through them, and leave in it some
mark of their action, too slight though it may be, at any
given moment, for analysis by means now at our disposal.

On the Gases contained in the Blood.

The gases contained in the blood are carbonic acid,
oxygen, and nitrogen, 100 volumes of blood containing
from 40 to 50 volumes of these gases collectively.

Arterial blood contains relatively more oxygen and less
carbonic acid than venous. But the absolute quantity of
carbonic acid is in both kinds of blood greater than that of

‘

90 DEVELOPMENT OF BLOOD.
the oxygen. The proportion of nitrogen is in both very
small. |

It is most probable that the carbonic acid of the blood
is partly in a state of simple solution, and partly in a state
of weak chemical combination. The portion of the car-
bonic acid which is chemically combined, is contained
partly in a bicarbonate of soda, and partly is united with
phosphate of the same base. ~The oxygen is combined
chemically with the hemoglobin of the red corpuscles
(pp. 75 and 85).

That the oxygen is absorbed chiefly by the red corpuscles
is proved by the fact that while blood is capable of
_ absorbing oxygen in considerable quantity, the serum
alone has little or no more power of absorbing this gas
than pure water.

Development of the Blood.

In the development of the blood little more can be traced
than the processes by which the corpuscles are formed.

The first formed blood-cells of the human embryo differ
much in their general characters from those which belong
to the latter periods of intra-uterine, and to all periods of
extra-uterine life. Their manner of origin differs also,
and it will be well perhaps to consider this first.
~ In the process of development of the embryo, the plan,
so to speak, of the heart and chief blood-vessels is first
laid out in cells. Thus the heart is at first but a solid
mass of cells, resembling those which constitute all other
parts of the embryo; and continuous with this are tracts
of similar cells—the rudiments of the chief blood-vessels.

The formation of the first blood corpuscles is very
simple. While the outermost of the embryonic cells, of
which the rudimentary heart and its attendant vessels are
composed, gradually develop into the muscular and other
tissues which form the walls of the heart and blood-vessels,
the inner cells simply separate from each other, and form

DEVELOPMENT OF BLOOD. QI

blood-cells; some fluid plasma being at the same time
secreted. Thus, by the same process, blood is formed, and
the originally solid heart and blood-vessels are hollowed out.

The blood-cells produced in this way, are from about
sss> tO zs Of an inch in diameter, mostly spherical,
pellucid, and colourless, with granular contents, and of
well-marked nucleus. Gradually, they acquire a red
colour, at the same time that the nucleus becomes more
defined, and the granular matter clears away. Mr. Paget
describes them, as, at this period, circular, thickly disc-
shaped, full-coloured, and, on an average, about =, of
an inch in diameter; their nuclei, which are about +, of
an inch in diameter, are central, circular, very little pro-
minent on the surfaces of the cell, and apparently slightly
granular or tuberculated.

Before the occurrence, however, of this change—from
the colourless to the coloured state—in many instances,
probably, during it, and in many afterwards, a process of
multiplication takes place by division of the nucleus and
subsequently of the cell, into two, and much more rarely,

Fig. 30.*

D ¥ F

three or four new cells, which gradually acquire ‘the
characters of the original cell from which they sprang
Fig. 30 (B, c, D, E).

* Fig. 30. Development of the first set of blood-corpuscles in the

92 DEVELOPMENT OF BLOOD,

When, in the progress of embryonic development, the
liver begins to be formed, the multiplication of blood-
cells in the whole mass of blood ceases, according to
Kolliker, and new blood-cells are produced by this organ.
Like those just described, they are at first colourless and
nucleated, but afterwards acquire the ordinary blood-
tinge, and resemble very much those of the first set. Like
them they may also multiply by division. In whichever
way produced, however, whether from the original for-
mative cells of the embryo, or by the liver, these coloured
nucleated cells begin very early in foetal life to be mingled
with coloured non-nucleated corpuscles resembling those of
the adult, and about the fourth or fifth month of embryonic
existence are completely replaced by them.

The manner of origin of these perfect non-nucleated
corpuscles must be now considered.

I. Concerning the cells from which they arise.

a. Before Birth—It is uncertain whether they are
derived only from the cells of the lymph, which, at about
the period of their appearance, begins to be poured into
the blood; or whether they are derived also from the
nucleated red cells, which they replace, or also from similar
nucleated cells, which K6lliker thinks are produced by the
liver during the whole time of foetal existence. —

b. After Birth.—Itis generally agreed that after birth the
red corpuscles are derived from the smaller of the nucleated
lymph or chyle-corpuscles,—the white corpuscles of the blood.

II. Concerning the Manner of their Development.

There is not perfect agreement among physiologists

mammalian embryo. A. A dotted, nucleated embryo-cell in process of
conversion into a blood-corpuscle ; the nucleus provided with a nucle-
olus. 3. A similar cell with a dividing nucleus ; at c, the division of
the nucleus is complete ; at p, the cell also is dividing. x. A blood-
corpuscle almost complete, but still containing a few granules. F. Per-
fect blood-corpuscle.

DEVELOPMENT OF BLOOD. 93

concerning the process by which lymph-globules or white
corpuscles (and in the foetus, perhaps the red. nucleated
cells) are transformed into red non-nucleated blood-cells.
For while ‘some maintain that the whole cell is changed
into a red one by the gradual clearing up of the con-
tents, including the nucleus, it is believed by Mr. Wharton
Jones and many others, that only the nucleus becomes the
red blood-cell, by escaping from its envelope and acquiring

_ the ordinary blood-tint.

Of these two theories, that which supposes the nucleus
of the lymph or chyle globule to be the germ of the future
red blood-corpuscle is the theory now generally adopted.

The development of red blood-cells from the corpuscles
of the lymph and chyle continues throughout life, and
there is no reason for supposing that after birth they have
any other origin.

Without doubt, these little bodies have, like all other
parts of the organism, a tolerably definite term of existence,
and in a like manner die and waste away when the portion
of work allotted to them has been performed. Neither the
length of their life, however, nor the fashion of their
decay, has been yet clearly made out, and we can only
surmise that in these things they resemble more or less
closely those parts of the body which lie more plainly
within our observation.

From what has been said, it will have appeared that when
the blood is once formed, its growth and maintenance are
effected by the constant repetition of the development of
new portions. Inthe same proportion that the blood yields
its materials for the maintenance and repair of the several
solid tissues, and for secretions, so are new materials sup-
plied to it in the lymph and chyle, and by development
made likeit. The part of the process which relates to the
formation of new corpuscles has been described, but it is
probably only a small portion of the whole process ; for the
assimilation of the new materials to the blood must be

‘

94 ASSIMILATION OF BLOOD.

perfect, in regard to all those immeasurable minute par-
ticulars by which the blood is adapted for the nutrition of
every tissue, and the maintenance of every peculiarity of
each. How precise the assimilation must be for such an
adaptation, may be conceived from some of the cases in —
which the blood is altered by disease, and by assimilation
is maintained in its altered state. For example, by the
insertion of vaccine matter, the blood is for a short time ,
manifestly diseased; however minute the portion of virus,
it affects and alters, in some way, the whole of the blood.
And the alteration thus produced, inconceivably slight as
it must be, is long maintained; for even very long after a
successful vaccination, a second insertion of the virus may
have no effect, the blood being no longer amenable to its
influence, because the new blood, formed after the vaccina-
tion, is made like the blood as altered by the vaccine
virus ; in other words, the blood exactly assimilates to its
altered self the materials derived from the lymph and chyle.
In health we cannot see the precision of the adjustment -
of the blood to the tissues; but we may imagine it from
the small influences by which, as in vaccination, it is
disturbed; and we may be sure that the new blood is as
perfectly assimilated to the healthy standard as in disease
it is assimilated to the most minutely altered standard.*
How far the assimilation of the blood is affected by any
formative power which it may possess in common with the
solid tissues, we know not. That this possible formative
power is, however, if present, greatly ministered to and
‘assisted by the actions of other parts there can be no doubt ;
as Ist, by the digestive and absorbent systems, and pro-
bably by the liver, and all of the so-called vascular glands ;
and, 2ndly, by the excretory organs, which separate from
the blood refuse materials, including in this term not only

* Corresponding facts in relation to the maintenance of the tissues
by assimilation will be mentioned in the chapter on NUTRITION .

;

USES OF THE BLOOD. | 95

the waste substance of the tissues, but also such matters
as, having been taken with food and drink, may have been
absorbed from the digestive canal, and have been sub-
sequently found unfit to remain in the circulating current.
And, 3rdly, the precise constitution of the blood is adjusted
by the balance of the nutritive processes for maintaining
the several tissues, so that none of the materials appro-
priate for the maintenance of any part may remain in
excess in the blood. Each part, by taking from the blood
the materials it requires for its maintenance, is, as has
been observed, in the relation of an excretory organ to all
the rest; inasmuch as by abstracting the matters proper
for its nutrition, it prevents excess of such matters as
effectually as if they were separated from the blood and
cast out altogether by the excreting organs specially present
for such a purpose.

Uses of the Blood.

‘The purposes of the blood, thus developed and main-
tained, appear, in the perfect state, to be these; Ist, to be
a source whencc the various parts of the body may abstract
the materials necessary for their nutrition and mainte-
nance; and whence the secreting organs may take the
materials for their various secretions; 2nd, to be a
constantly replenished store-house of latent chemical force,
which in its expenditure will maintain the heat of the
body, or be transformed by the living tissues, and mani-
fested by them in various forms as vital power; 3rd, to
convey oxygen to the several tissues which may need it,
either for the discharge of their functions, or for combination
with their refuse matter ; 4th, to bring from all parts refuse
matters, and convey them to places whence they may be dis-
charged; 5th, to warm and moisten all parts of the body.

Uses of the various Constituents of the Blood.

Regarding the uses of the various constituents of the

96 USES OF THE BLOOD. |

blood it may be said that the matter almost resolves itself
into an analysis of the different parts of the body, and of
the food and drink which are taken for their nutrition,
with a subsequent consideration of how far any given con-
stituent of the blood may be supposed to be on its way
to the living tissues, to be incorporated with and nourish
them, or, having fulfilled its purpose, to be on its way ina
more or less changed condition to the excretory organs to be
cast out. It must be remembered, however, that the blood
contains also matters which serve by their combustion
to produce heat, and, again, others which possibly sub-
serve only a mechanical, although most important, purpose ;
as for instance the preservation of the due specific gravity
of the blood, or some other quality by which it is enabled
to maintain its proper relation to the vessels containing it
and to the tissues through which it passes. Lastly, among
the constituents of the blood, are the gases, oxygen and
carbonic acid, and the substances specially adapted to carry
them, which can scarcely be said to take part in the nutri-
tion of the body, but are rather the means and evidence of
the combustion before referred to, on which, to a great

extent, directly or indirectly, all vitality depends.
Albumen.—The albumen, which exists in so large a

proportion among the chief constituents of the blood, is
without doubt mainly for the nourishment of those tex-
tures which contain it or other compounds nearly allied to it.
Besides its purpose in nutrition, the albumen of the liquor
sanguinis is doubtless of importance also in the maintenance
of those essential physical properties of the blood to which
reference has been already made.

Fibrin.—It has been mentioned in a previous part of
this chapter that the idea of fibrin existing in the blood,
as fibrin, is probably founded in error ; and that it is formed
in the act of coagulation by the union of two substances,
which before existed separately (p. 64). In considering,
therefore, the functions of fibrin, we may exclude the notion

a

USES OF BLOOD. | 97

of its existence, as such, in the blood in a fluid state, and of
its use in the nutrition of certain special textures, and look
for the explanation of its functions to those circumstances,
whether of health or disease, under which it is produced.

‘In hemorrhage, for example, the formation of fibrin in the

clotting of blood, is the means by which, at least for a
time, the bleeding is restrained or stopped; and the material
which is produced for the permanent healing of the injured
part, contains a coagulable material probably identical, or
very nearly so, with the fibrin of clotted blood.

‘atty Matters.—The fatty matters of the blood subserve
more than one purpose. For while they are the means, at
least in part, by which the fat of the body, so widely dis-
tributed in the proper adipose and other textures, is re-
plenished, they also, by their union with oxygen, assist in
maintaining the temperature of the body. In certain secre-
tions also, notably the milk and bile, fat is an important
constituent. | |

' Saline Matter—The uses of the saline constituents of
the blood are, first, to enter into the composition of such
textures and s2cretions as naturally contain them, and,
secondly, to assist in preserving the due specific gravity
and alkalinity of the blood and, perhaps, also in preventing
its decomposition. The phosphate and carbonate of sodium,
besides maintaining the alkalinity of the blood, are said
especially to preserve the liquidity of its albumen, and to
favour its circulation through the capillaries, at the same
time that they increase the absorptive power of the serum
for gases. But although, from the constant presence of a
certain quantity of saline matter in the blood, we may
believe that it has these last-mentioned important functions
in connection with the blood itself, apart from the nutri-
tion of the body, yet, from the amount which is daily
separated by the different excretory organs, and especially
by the kidneys, we must also believe that a considerable
quantity simply passes through the blood, both from the

H

98 | USES OF BLOOD.

food and from the tissues, as a temporary and useless con -
stituent, to be excreted when opportunity offers.
Corpuscles.—The uses of the red corpuscles are probably
not yet fully known, but they may be inferred, at least in
part, from the composition and properties of their contents.
The affinity of hemoglobin for oxygen has been already
' mentioned; and the main function of the red corpuscles
seems to be the absorption of oxygen in the lungs by
means of this constituent, and its conveyance to all parts of
the body, especially to those tissues, the nervous and mus-
- cular, the discharge of whose functions depends in so great
a degree upon a rapid and full supply of this element.
The readiness with which hemoglobin absorbs oxygen, and

delivers it up again to a reducing agent, so well shown by —

the experiments of Prof. Stokes, admirably adapts it for
this purpose. How far the red corpuscles are concerned
in the nutrition of the tissues is quite unknown.

The relation of the white to the red corpuscles of the
blood has been already considered (p. 92); of the functions
of the former, other than are concerned in this relationship,
nothing is positively known. Recent observations of the
migration of the white corpuscles from the interior of the
blood-vessels into the surrounding tissues (see Section, On
the Circulation in the Capillaries) have, however, opened
out a large field for investigation of their probable fune-
tions in connection with the nutrition of the textures,
in which, even in health, they appear to wander.

gts elt tee AS

a te

A att

THE CIRCULATION. 99

CHAPTER VI.
CIRCULATION OF THE BLOOD.

Tux body is divided into two chief cavities—the chest or
thorax and abdomen, by a curved muscular partition, called
the diaphragm (fig. 31). The chest’is almost entirely filled
by the lungs and heart; the latter being fitted in, so to
speak, between the two lungs, nearer the front than
- the back of the chest, and partly overlapped by them
(fig. 31). Each of these organs is contained in a distinct
bag, called respectively the right and left pleura and the
pericardium, the latter being fibrous in the main, but lined
on the inner aspect by a smooth shining epithelial covering,
on which can glide, with but little friction, the equally
smooth surface of the heart enveloped by it. In fig. 31
the containing bags of pleura and pericardium are sup-
posed to have been removed, Entering the chest from
above is a lerge and long air-tube, called the trachea,
which divides into two branches, one for each lung, and
through which air passes and repasses in respiration,
Springing from the upper part or base of the heart may be
seen the large vessels, arteries, and veins, which convey
blood either to or from this organ.

In the living body the heart and lungs are in constant
rhythmic movement, the result of which is an unceasing
stream of air through the trachea alternately into and out
of the lungs, and an unceasing stream of blood into and
- out of the heart.

It is with this last event that we are concerned especially
in this chapter,—with the means, that is to say, by which
the blood which at one moment is forced out of the heart,
is in a few moments more returned to it, again to depart,
and again pass through the body in course of what is

H 2

100 THE CIRCULATION.

technically called the circulation. The purposes for which

this unceasing current is maintained, are indicated in the

uses of the blood enumerated in the preceding chapter.
The blood is conveyed away from the heart by the

arteries, and returned to it by the veins; the arteries and.

veins being continuous with each other, at one end by
means of the heart, and at the other by a fine network of
vessels called the capillaries. The blood, therefore, in its
passage from the heart passes first into the arteries, then
into the capillaries, and lastly into the veins, by which it
is conveyed back again to the heart,—thus completing a
revolution, or circulation.

Fig. 31.*

As generally described there are two circulations by
which all the blood must pass; the one, a shorter circuit

* Fig, 31. View of heart.and lungs in situ. The front portion of
the chest-wall, and the outer or parietal layers of the pleure and peri-
cardium have been removed. The lungs are partly collapsed.

>t ee

a

THE CIRCULATION. IOI

from the heart to the lungs and back again; the other and
larger circuit, from the heart to all parts of the body and
back again; but more strictly speaking, there is only one
complete circulation, which may be diagrammatically repre-
sented by a double loop, as in the accompanying figure.
On reference to Fig. 32.*

this figure and
noticing the di-
rection of the ar-
rows which repre-
sent the course
of the stream
of blood, it will
be observed that
while there is a
smaller and a
larger circle both
of which pass
through the heart,
yet that these are
not distinct, “one
from the other,
but are formed
really by one con-
tinuous’ stream,
the whole of
which must, at i [7 _ 77
one part of ‘its course, pass through the lungs. Subor-
dinate to the two principal circulations, the pulmonary and
systemic as they are named, it will be noticed also in the
same figure, that there is another, by which a portion
of the stream of blood having been diverted once into
the capillaries of the intestinal~canal, and some other
organs, and gathered up again into a single stream, is a
second time divided in its passage through the liver,

* Fig. 32. Diagram of the circulation.

102 THE CIRCULATION.

before it finally reaches the heart and completes a revolu-
tion. This subordinate stream through the liver is called
the portal circulation.

The principal force provided for constantly moving the
blood through this course is that of the muscular substance
of the heart; other assistant forces are (2) those of the
elastic walls of the arteries, (3) the pressure of the muscles
among which some of the veins run, (4) the movements of
the walls of the chest in respiration, and probably, to some
extent, (5), the interchange of relations between the blood
and the tissues which ensues in the capillary system during
the nutritive processes. The right direction of the blood’s.
course is determined and maintained by the valves of the
heart to be immediately described; which valves open to
permit the movement of the blood in the course described,
but close when any force tends to move it in the contrary
direction.

We shall consider separately each member of the system
of organs for the circulation: and first—

The Heart.

The heart is a hollow muscular organ, the interior of
which is divided by a partition in such a manner as to
form two chief chambers as cavities—right and left. Each
of these chambers is again subdivided into an upper and
a lower portion called respectively the auricle and ventricle,
which freely communicate one with the other ; the aperture
of communication, however, being guarded by valvular
curtains, so disposed so as to allow blood to pass freely from
theauricle into the ventricle, but not in the opposite direc-
tion. There are thus four cavities altogether in the heart
—two auricles and two ventricles; the auricle and ventricle
of one side being quite separate from those of the other.
The right auricle communicates, on the one hand, with the
veins of the general system, and, on the other, with the
right ventricle, while the latter leads directly into the pul-
monary artery, the orifice of which is guarded by valves.

THE HEART. 103
The eft auricle again communicates, on the one hand, with
the pulmonary veins, and on the other, with the left
ventricle, while the latter leads directly i
large artery which conveys blood to the general system,
the orifice of which, like that of the pulmonary artery, is
guarded by valves.

The arrangement of the heart’s valves is such that
the blood can pass only in one definite direction, and
this is as follows (fig. 33):—From the right auricle
the blood passes into the right ventricle, and thence
into the pulmo-
nary artery, by
which it is con-
veyed to the ca- |
pillaries of the |
lungs. From the |
lungs the blood, |
whichis nowpuri- |
fied and altered |
in colour, is ga-
thered by thepul-
monary veins and |
taken to the left
auricle. Fromthe
left auricle it |
passes into the |
left ventricle, and
thence into the L ———_a_—
aorta, by which it is distributed to the capillaries of every
portion of the body. The branches of the aorta, from
being distributed to the general system, are called systemic
arteries; and from these the blood passes into the sys-
temic capillaries, where it again becomes dark and impure,
and thence into the branches of the systemic veins, which

* Fig. 33. Diagram of the circulation through the heart (after Dalton)

104 THE CIRCULATION.

forming by their union two large trunks, called the supe-
rior and inferior vena cava, discharge their contents into
the right auricle, whence we supposed the blood to start

(fig. 33).
Structure of the Valves of the Heart.

It will be well now to consider the structure of the

Fig. 34.*

* Fig. 34. The right auricle and ventricle opened, and a part of

their right and anterior walls removed, so as to show their interior. 4.
—lI, superior vena cava; 2, inferior vena cava; 2’, hepatic veins cut
short ; 3, right auricle; 3’, placed in the fossa ovalis, below which is
the Eustachian valve ; 3", is placed close to the aperture of the coronary

STRUCTURE OF HEART’S VALVES. 105

valves of the heart, and the manner in which they perform
their function of directing the stream of blood in the
course which has been just described. The valve between
the right auricle and ventricle is named tricuspid (fig. 34),
because it presents three principal cusps or pointed portions,
and that between the left auricle and ventricle bicuspid or
mitral, because it has two such portions (fig. 35). But in
both valves there is between each two principal portions a
smaller one; so that more properly, the tricuspid may be
described as consisting of six, and the mitral of four, por-
tions. Each portion is of triangular form, its apex and
sides lying free in the cavity of the ventricle, and its base,
which is continuous with the bases of the neighbouring
portions, so as to form an annular membrane around the
auriculo-ventricular opening, being fixed to a tendinous
ring, which encircles the orifice between the auricle and
ventricle, and receives the insertions of the muscular fibres
of both. In each principal portion of the valve may be
distinguished a middle-piece, extending from its base to
its apex, and including about half its width; this piece
is thicker, and: much tougher and tighter than the border-

_ pieces which are attached loose and flapping at its sides.
While the bases of the several portions of the valves
are fixed to the tendinous rings, their ventricular surfaces

vein; +, +, placed in the auriculo-ventricular groove, where a narrow
portion of the adjacent walls of the auricle and ventricle has been pre-
‘served ; 4, 4, cavity of the right ventricle, the upper figure is imme-
diately below the semilunar valves ; 4’, large columna carnea or mus-
culus papillaris ; 5, 5’, 5", tricuspid valve ; 6, placed in the interior of
the pulmonary artery, a part of the anterior wall of that vessel having
been removed, and a nayrow portion of it preserved at its commence-
ment where the semilunar valves are attached; 7, concavity of the aortic
arch close to the cord of the ductus arteriosus ; 8, ascending part or
sinus of the arch covered at its commencement by the auricular appendix
and pulmonary artery ; 9, placed between the innominate and left carotid
arteries ; 10, appendix of the left auricle ; 11, 11, the outside of the left
ventricle, the lower figure near the apex. (From Quain’s Anatomy.)

106 THE CIRCULATION.

and borders are fastened by slender tendinous fibres, the
chord@ tendinea, to the walls of the ventricles, the muscular
fibres of which project into the ventricular cavity in the

Fig. 35.*

* Fig. 35. The left auricle and ventricle opened and a part of their
anterior and left walls removed so as to show theirinterior. 4.—The
pulmonary artery has been divided at its commencement so as to show
the aorta ; the opening into the left ventricle has been carried a short
distance into the aorta between two of the segments of the semilunar
valves ; the left part of the auricle with its appendix has been removed.

STRUCTURE OF HEART’S VALVES. 107

form of bundies or columns—the columne@ carnee. These
columns are not all of them alike, for while some of them
are attached along their whole length on one side, and
by their extremities, others are attached only by their
extremities; and a third set, to which the name musculi
papillares has been given, are attached to the wall of the
ventricle by one extremity only, the other projecting,
papilla-like, into the cavity of the ventricle (5, fig. 35), and
having attached to it chorde tendinee. Of the tendinous
cords, besides those which pass from the walls of the ven-
tricle and the musculi papillares, to the margins of the valves
both free and attached, there are some of especial strength,
which pass from the same parts to the edges of the middle
pieces of the several chief portions of the valve. The
ends of these cords are spread out in the substance of the
valve, giving its middle piece its peculiar strength and
toughness; and from the sides numerous other more
slender and branching cords are given off, which are

The right auriele has been thrown out of view. 1, the two right pul-
monary veins cut short’; their openings are seen within the auricle ;
1’, placed within the cavity of the auricle on the left side of the septum
and on the part which forms the remains of the valve of the foramen

: ovale, of which the crescentic fold is seen towards the left hand of 1’ ;

2, a narrow portion of the wall of the auricle and ventricle preserved
round the auriculo-ventricular orifice ; 3, 3/, the cut surface of the walls
of the ventricle, seen to become very much thinner towards 3", at the
apex ; 4, a small part of the anterior wall of the left ventricle which
has been preserved with the principal anterior columna carnea or
musculus papillaris attached to it; 5, 5, musculi papillares ; 5’, the
left side of the septum between the two ventricles, within the cavity of
the left ventricle; 6, 6, the mitral valve ; 7, placed in the interior of
the aorta near its commencement and above the three segments of its
semilunar valve which are hanging loosely together ; 7’, the exterior of
the great aortic sinus ; 8, the root of the pulmonary artery and its
semilunar valves ; 8’, the separated portion of the pulmonary artery
remaining attached to the aorta by 9, the cord of the ductus arteriosus ;
10, ‘the arteries rising from the summit of the aortic arch. (From
Quain’s Anatomy.)

108 THE CIRCULATION.

attached all over the ventricular surface of the adjacent
border-pieces of the principal portions of the valves, as
well as to those smaller portions which have been mentioned
as lying between each two principal ones. Moreover, the
musculi papillares are so placed that from the summit of
each tendinous cords may proceed to the adjacent halves of
two of the principal divisions, and to one intermediate or
smaller division, of the valve.

It has been already said that while the ventricles com-
municate, on the one hand, with the auricles, they communi-
cate, on the other, with the large arteries which convey the
blood away from the heart; the right ventricle with the pul-
monary artery (6, fig. 34), which conveys blood to the lungs,
and the left ventricle with the aorta, which distributes it
to the general system (7, fig. 35). And as the auriculo-
ventricular orifice is guarded by valves, so are also the
mouths of the pulmonary artery and aorta (figs. 34, 35).

The valves, three in number, which guard the orifice of
each of these two arteries, are called the semilunar valves.
They are nearly alike on both sides of the heart; but those
of the aorta are altogether thicker and more strongly con-
structed than those of the pulmonary artery. Like the
tricuspid and mitral valves, they are formed by a dupli-
cature of the lining membrane of the heart, strengthened
by fibrous tissue. Each valve is of semilunar shape, its
convex margin being attached to a fibrous ring at the
place of junction of the artery to the ventricle, and the
concave or nearly straight border being free (fig. 35). In
the centre of the free edge of the valve, which contains a
fine cord of fibrous tissue, is a small fibrous nodule, the

corpus Arantii, and from this and from the attached border .

fine fibres extend into every part of the mid substance of
the valve, except a small lunated space just within the
free edge, on each side of the corpus Arantii. Here the
valve is thinnest, and composed of little more than the
endocardium. Thus constructed and attached, the three

any, ay all

ACTION OF THE HEART. 109

semilunar valves are placed side by side around the arterial
orifice of each ventricle, so as to form three little pouches,
which can be thrown back and flattened by the blood pass-
ing out of the ventricle, but which belly out immediately
so as to prevent any return (6, fig. 34). This will be again
referred to immediately.

The muscular fibres of the heart; unlike those of most
involuntary muscles, present a striated appearance under
the microscope. (See Chapter on Motion.)

THE ACTION OF THE HEART.

The heart’s action in propelling the blood consists in the
successive alternate contractions and dilatations of the mus-
cular walls of its two auricles and two ventricles. The
auricles contract simultaneously ; so do the ventricles ; their
dilatations also are severally simultaneous; and the con-
tractions of the one pair of cavities are synchronous with
the dilatations of the other.

- The description of the action of the heart may best be
commenced at that period in each action whichimmediately
precedes the beat of the heart against the side of the chest,
and, by a very small interval more, precedes the pulse at
the wrist. For at this time the whole heart is in a passive
state, the walls of both auricles and ventricles are relaxed,
and their cavities are being dilated. The auricles are
gradually filling with blood flowing into them from the
veins ; and a portion of this blood passes at once through
them into the ventricles, the opening between the cavity
of each auricle and that of its corresponding ventricle
being, during all the pause, free and patent. The auricles,
however, receiving more blood than at once passes through
them to the ventricles, become, near the end of the pause,
fully distended ; then, in the end of the pause, they con-
tract and empty their contents into the ventricles. The
contraction of the auricles is sudden and very quick; it
commences at the entrance of the great veins into them,

|

ns

————

|

110. THE CIRCULATION.

and is thence propagated towards the ariculo-ventricular
opening; but the last part which contracts is the aricular
appendix. The effect of this contraction of the auricles is
to propel nearly the whole of their blood into the ventricles.
The reflux of blood into the great veins is resisted not only
by the mass of blood in the veins and the force with which
it streams into -the auricles, but also by the simultaneous
contraction of the muscular coats with which the large
veins are provided for some distance before their entrance
into the auricles; a resistance which, however, is not so
complete but that a small quantity of blood does regurgi4
tate, i.e., flow backwards into the veins, at each auricular
contraction. The effect of this regurgitation from the
right auricle is limited by the valves at the junction of the
subclavian and internal jugular veins, beyond which the
blood cannot move backwards; and the coronary vein, or
vein which brings back to the right auricle the blood
which has circulated in the substance of the heart, is pre-
served from it by a valve at its mouth.

The blood which is thus driven, by the contraction of the
auricles, into the corresponding ventricles, being added to
that which had already flowed into them during the heart’s
pause, is sufficient to complete the dilatation or diastole of
the ventricles. Thus distended, they immediately contract :
so immediately, indeed, that their contraction, or systole,
looks as if it were continuous with that of the auricles.
This has been graphically described by Harvey in the
following passage :—‘‘ These two motions, one of the ven-
tricles, another of the auricles, take place consecutively,
but in such a manner that there is a kind of harmony, or
rhythm, present between them, the two concurring in such
wisethat but one motion is apparent; especially in the
warmer blooded animals, in which the movements in ques-
tion arerapid. Nor is this for any other reason than it is
in a piece of machinery, in which, though one wheel gives
motion to another, yet all the wheels seem to move simul-

hes taps
pee Ore ae

ACTION OF THE HEART. III

taneously; or in that mechanical contrivance which is
adapted to fire-arms, where the trigger being touched,
down comes the flint, strikes against the steel, elicits a
spark, which, falling among the powder, it is ignited, upon
which the flame extends, enters the barrel, causes the
explosion, propels the ball, and the mark is attained—all
of which incidents ; by reason of the celerity with which
they happen, seem to take place in the twinkling of an
eye.” .The ventricles contract much more slowly than
the auricles, and in their contraction, probably always
thoroughly empty themselves, differing in this respect from
the auricles, in which even after their complete contrac-
tion, a small quantity of blood remains. The form and
position of the fleshy columns on the internal walls of the
ventricle appear, indeed, especially adapted to produce this
obliteration of their cavities during their contraction; and the
completeness of the closure may often be observed on making
a transverse section of a heart shortly after death, in any case
in which the contraction of the rigor mortis is very marked.
In such a case, only a central fissure may be discernible to
the eye in the place of the cavity of each ventricle.

At the same time that the walls of the ventricles con-
tract, the fleshy columns, and especially those of them
called the musculi papillares, contract also, and assist in
bringing the margins of the auriculo-ventricular valves
into apposition, so that they close the auriculo-ventricular
openings, and prevent the backward passage of the blood
into the auricles (p. 113). The whole force of the ven-
tricular contraction is thus directed to the propulsion of
the blood through their arterial orifices. During the time
which elapses between the end of one contraction of the
ventricles, and the commencement of another, the com-
munication between them and the great arteries—the aorta
on the left side, the pulmonary artery on the right—is
closed by the three semilunar valves situated at the orifice
of each vessel. But the force with which the current of

I12 : THE CIRCULATION.

blood is propelled by the contraction of the ventricle sepa-
rates these valves from contact with each other, and presses
them back against the sides of the artery, making a free
passage for the stream of blood. Then, assoon as the ven-
tricular contraction ceases, the elastic walls of the distended
artery recoil, and, by pressing the blood behind the valves,
force them down towards the centre of the vessel, and spread
them out so as to close the orifice and prevent any of the
blood flowing back into the ventricles (p. 118).

As soon as the auricles have completed their contraction
they begin again to dilate, and to be refilled with blood,
which flows into them in a steady stream through the
great venous trunks. They are thus filling during all the
time in which the ventricles are contracting ; and the con-
traction of the ventricles being ended, these also again
dilate, and receive again the blood that flows into them
from the auricles. By the time that the ventricles are
thus from one-third to two-thirds full, the auricles are~
distended; these, then suddenly contracting, fill up the
ventricles, as already described.

If we suppose a cardiac revolution, which includes the
contraction of the auricles, the contraction of the ventricles, .
and their repose, to occupy rather more than a second, the

following table will represent, in tenths of a second, the
time occupied by the various events we have considered.

Contraction of Auricles . . 1+Repose of Auricles . . I0O=11
a Ventricles . 4+ ,, Ventrieles . 7F=18
Repose (no contraction of .
eitherauricles orventricles) 6+Contraction (of either

— auricles or ventricles) 5=I11
II

Action of the Valves of the Heart.

The periods in which the several valves of the heart are
in action may be connected with the foregoing table; for
the auriculo-ventricular valves are closed, and the arterial
valves are open during the whole time of the ventricular
contraction, while, during the dilatation and distension of

FUNCTION OF THE VALVES. 113
the ventricles the latter valves are shut, the former open.
Each half or side of the heart, through the action of its
valves, may. be Fig. 36.*

compared with a
kind of forcing
pump like the
common enema-
syringe with two
valves, of which
one admits the
fluid on raising
the piston, but
is closed again
when the piston
is forced down;
while. the other
opens for the es-
cape of the fluid,
but closes when
the piston is
raised, so as, to
prevent the re-
gurgitation of the
fluid already
forced through it.
The ventricular
dilatation is here
represented by
the raising-up of
the piston; the
valve thus admit-
ting fluid repre-
sents the auriculo-
ventricular valve,
which is closed

* Fig. 36. Diagrams of valves of the heart (after Dalton).
I

114 THE CIRCULATION.

again when the piston is forced down, i.e., when the ven-
tricle contracts, and the other, é.e., the arterial, valve
opens. The diagrams on the preceding page illustrate this
very well.

During auricular contraction, the force of the blood pro-
pelled into the ventricle is transmitted in all directions, but
being insufficient to raise the semilunar valves, it is ex-
pended in distending the ventricle, and in raising and
gradually closing the auriculo-ventricular valves, which,
when the ventricle is full, form a complete septum between
it and the auricle. This elevation of the auriculo-ventricular
valves is, no doubt, materially aided by the action of the
elastic tissue which Dr. Markham has shown to exist so
largely in their structure, especially on the auricular sur-
face. When the ventricle contracts, the edges of the valves
are maintained in apposition by the simultaneous contrac-
tion of the musculi papillares, which are enabled thus to act
by the arrangement of their tendinous cords just men-
tioned. In this position the segments of the valves are
held secure, even though the form and size of the orifice
and the ventricle may change during the continued con-
traction ; for the border pieces are held by their mutual
apposition and the equal pressure of the blood on their
ventricular surfaces; and the middle pieces are secure by
their great strength, and by the attachment of the ten-
dinous cords along their margins, these cords being always
held tight by the contraction of the musculi papillares. A
peculiar advantage, derived from the projection of these
columns into the cavity of the ventricle, seems to be, that
they prevent the valve from being converted into the auricle;
for, when the ventricle contracts, and the parts of its walis
to which, through the medium of the columns, the ten-
dinous cords are affixed, approach the auriculo-ventricular
orifices, there would be a tendency to slackness of the:
cords, and the valves might be everted, if it were not that
while the wall of the ventricle is drawn towards the orifice,

CETUS ES rah, We

ae

FUNCTION OF THE VALVES. {15

the end of the simultaneously contracting fleshy column is
drawn away from it, and the cords are held tight.

What has been said applies equally to the auriculo-
ventricular valves on both sides of the heart, and of both
alike the closure is generally complete every time the
ventricles contract. But in some circumstances, the closure
of the tricuspid-valve is not complete, and a certain
quantity of blood is forced back into the auricle: and,
since this may be advantageous, by preventing the over-
filling of the vessels of the lungs, it has been called the
safety-valve action of this valve (Hunter, Wilkinson King).
The circumstances in which it usually happens are those in ,
which the vessels of the lung are already full enough when
the right ventricle contracts, as ¢.g., in certain pulmonary \
diseases, in very active exertion, and in great efforts. In|
these cases, perhaps, because the right ventricle cannot
contract quickly or completely enough, the tricuspid valve
does not completely close, and the regurgitation of blood
may be indicated by a pulsation in the jugular veins syn-
chronous with that in the carotid arteries.

The arterial or semilunar valves are, as already said,
brought into action by the pressure of the arterial blood
forced back towards the ventricles, when the elastic walls
of the arteries recoil after being dilated by the blood pro-
pelled into them in the previous contraction of the ventricle.
The dilatation of the arteries is, in a peculiar manner,
adapted to bring the valves into action. The lower borders
of the semilunar valves are attached to the inner surface of
a tendinous ring, which is, as it were, inlaid, at the orifice
of the artery, between the muscular fibres of the ventricle
and the elastic fibres of the walls of the artery. The tissue
of this ring is tough, does not admit of extension under
such pressure as it is commonly exposed to; the valves are
equally inextensile, being, as already mentioned, formed
of tough, close-textured, fibrous tissue, with strong inter-

woven cords, and covered with endocardium. Hence, when
I 2

116 THE CIRCULATION,

the ventricle propels blood through the orifice and into the
canal of the artery, the lateral pressure which it exercises
is sufficient to dilate the walls of the artery, but not
enough to stretch in.an equal degree, if at all, the unyield-
ing valves and the ring to which their lower borders are
attached. The effect, therefore, of each such propulsion
of blood from the ventricle is, that the wall of the first
portion of the artery is dilated into three pouches behind
the valves, while the free margins of the valves, which had
previously lain in contact with the inner surface of the
artery (as at a, fig. 37), are drawn inward towards its

Fig. 37.*

centre (fig. 37, B). Their positions may be explained by
the foregoing diagrams, in which the continuous lines
represent a transverse section of the arterial walls, the
dotted ones the edges of the valves, firstly, when the valves
are in contact with the walls (A), and, secondly, when the
walls being dilated, the valves are drawn away from
them (8).

This position of the valves and arterial walls is retained
so long as the ventricle continues in contraction: but, so-

| * Fig. 37. Sections of aorta, to show the action of the semilunar
valves. A is intended to show the valves, represented by the dotted
lines, in contact with the arterial walls, represented by the continuous
outer line. 3B (after Hunter) shows the arterial wall distended into
three pouches (@), and drawn away from the valves which are straight-
ened into the form of equilateral triangle, as represented by the dotted
lines.

rt

eg aye ee
; :

FUNCTION OF THE VALVES. 117

soon as it relaxes, and the dilated arterial walls can recoil
by their elasticity, they press the blood as well towards the
ventricles as onwards in the course of the circulation. Part
of the blood thus pressed back lies in the pouches (a, fig.
37, B) between the valves and the arterial walls; and the
valves are by it pressed together till their thin lunated
margins meet in three lines radiating from the centre to
the circumference of the artery (7 and 8, fig. 38).

* Fig. 38. View of the base of the ventricular part of the heart,
showing the relative position of the arterial and auriculo-ventricular
orifices.—3. The muscular fibres of the ventricles are exposed by the
removal of the pericardium, fat, blood-vessels, etc. ; the pulmonary
artery and dorta have been removed by a section made immediately
beyond the attachment of the semilunar valves, and the auricles have
been removed immediately above the auriculo-ventricular orifices. The
semilunar and auriculo-ventricular valves are in the nearly closed con-
dition. 1, 1, the base of the right ventricle ; 1’, the conus arteriosus ;
2, 2, the base of the left ventricle ; 3, 3, the divided wall of the right
auricle ; 4, that of the left ; 5, 5’, 5", the tricuspid valve ; 6, 6’, the
mitral valve. In the angles between these segments are seen the
smaller fringes frequently observed ; 7, the anterior part of the pul-
monary artery ; 8, placed upon the posterior part of the root of the
aorta; 9, the right, 9’, the left coronary artery. (From Quain’s
Anatomy.)

118 THE CIRCULATION.

Mr. Savory has clearly shown that this pressure of the
blood is not entirely sustained by the valves alone, but in
part by the muscular substance of the ventricle. Availing

himself of a method of dissection
hitherto apparently overlooked,
namely, that of making vertical
sections (fig. 39) through various
parts of the tendinous rings, he
has been enabled to show clearly
‘that the aorta and pulmonary
artery, expanding towards their
termination, are situated upon the
outer edge of the thick upper border
of the ventricles, and that conse-
quently the portion of each semi-
lunar valve adjacent to the vessel
passes over and rests upon the muscular substance—being
thus supported, as it were, on a kind of muscular floor
formed by the free border of the ventricle. The result of
this arrangement will be that the reflux of the blood will
be most efficiently sustained by the ventricular wall.y

The effect of the blood’s pressure on the valve is, as said,
to cause their margins to meet in three lines radiating from
the centre to the circumference (7 and 8, fig. 38). The con-
tact of the valve in this position, and the complete closure
of the arterial orifice, are secured by the peculiar construc-
tion of their borders before mentioned. Among the cords
which are interwoven in the substance of the valves, are
two of greater strength and prominence than the rest; of .
which one extends along the free border of each valve, and

Fig. 39*.

is

* Fig. 39. Vertical section through the aorta at its junction with
the left.ventricle. 1. Section of arterial coat. 2. Section of valve.
3. Section of ventricle.

+ Mr, Savory’s preparations, illustrating this and other points in
relation to the structure and functions of the valves of the heart, are in
the museum of St. Bartholomew’s Hospital.

~

SOUNDS OF THE HEART. IIQ

the other forms a double curve or festoon just below the
free border. Each of these cords is attached by its outer
extremities to the outer end of the free margin of its valve,
and in the middle to the corpus Arantii; they thus enclose
a lunated space from a line to a line and a half in width,
in which space the substance of the valve is much thinner
and more pliant than elsewhere. When the valves are
pressed down, all these parts or spaces of their surfaces
come into contact, and the closure of the arterial orifice is
' thus secured by the apposition not of the mere edges of the
valves, but of all those thin lunated parts of each, which
lie between the free edges and the cords next below them.
These parts are firmly pressed together, and the greater
the pressure that falls on them, the closer and more secure
is their apposition. Thecorpora Arantii meet at the centre |
of the arterial orifice when the valves are down, and they
probably assist in the closure; but they are not essential
to it, for, not unfrequently, they are wanting in the valves
of the pulmonary artery, which are then extended in larger,
thin, flapping margins. In valves of this form, also, the
inlaid cords»are less distinct than in those with corpora
Arantii; yet the closure by contact of their surfaces is not
less secure.

Sounds of the Heart.

When the ear is placed over the region of the heart, two
sounds may be heard at every beat of the heart, which
follow in quick succession, and are succeeded by a pause
or period of silence. The first sound is dull and pro-
longed ; its commencement coincides with the impulse of
the heart, and just precedes the pulse at the wrist. The
second is a shorter and sharper sound, with a somewhat
flapping character, and follows close after the arterial pulse.
The period of time occupied respectively by the two sounds
taken together, and by the pause, are almost exactly equal.

120 THE CIRCULATION.

The relative length of time occupied by each sound, as
compared with the other, is a little uncertain. The difference
may be best appreciated by considering the different forces
concerned in the production of the two sounds. In one case
there is a strong, comparatively slow, contraction of a
large mass of muscular fibres, urging forward a certain
quantity of fluid against considerable resistance ; while in

- the other it is a strong but shorter and sharper recoil of

the elastic coat of the large arteries,—shorter because
‘there is no resistance to the flapping back of the semilunar
valves, as there was to their opening. The difference may
be also expressed, as Dr. C. J. B. Williams has remarked,
by saying the words lwbhb—dup.

The events which correspond, in point of time, with the
first sound, are the contraction of the ventricles, the first
part of the dilatation of the auricles, the closure of the
auriculo-ventricular valves, the opening of the semilunar
valves, and the propulsion of blood into the arteries. The
sound is succeeded, in about one-thirtieth of a second, by
the pulsation of the facial artery, and in about one-sixth
of a second, by the pulsation of the arteries at the wrist.
The second sound, in point of time, immediately follows
the cessation of the ventricular contraction, and corresponds
with the closure of the semilunar valves, the continued
dilatation of the auricles, the commencing dilatation of the
ventricles, and the opening of the auriculo-ventricular
valves. The pause immediately follows the second sound,
and corresponds in its first part with the completed disten-
sion of the auricles, and in its second with their contraction,
and the distension of the ventricles, the auriculo-ventricular
valves being all the time open, and the arterial valves
closed.

The chief cause of the first sound of the heart appears

to be the vibration of the auriculo-ventricular valves, and —

also, but to a less extent, of the ventricular walls, and

coats of the aorta and pulmonary artery, all of which parts

SOUNDS OF THE HEART. I2I

are suddenly put into a state of tension at the moment of
ventricular contraction.

This view, long ago advanced by Dr. Billing, is sup-
ported by the fact observed by Valentin, that if a portion
of a horse’s intestine, tied at one end, be moderately filled
with water, without any admixture of air, and have a
syringe containing water fitted to the other end, the first
sound of the heart is exactly imitated by forcing in more
water, and thus suddenly rendering the walls of the intes-
tine more tense.

The cause of the second sound is more simple than
that of the first. It is probably due entirely to the
sudden closure and consequent: vibration of the semilunar
valves when they are pressed down across the orifices of
the aorta and pulmonary artery; for, of the other events,
which take place during the second sound, none is cal-
culated to produce sound. ‘The influence of the valves
in producing the sound, is illustrated by the experiment
already quoted from Valentin, and from others performed
on large animals, such as calves, in which the results could
be fully appreciated. In these experiments two delicate
curved needles were inserted, one into the aorta, and another
into the pulmonary artery, below the line of attachment of
the semilunar valves, and, after ‘being carried upwards
about half an inch, were brought out again through the
coats of the respective vessels,.so that in each vessel one
valve was included between the arterial walls and the wire.
Upon applying the stethoscope to the vessels, after such
an operation, the second sound had ceased to be audible.
_ Disease of these valves, when so extensive as to interfere
with their efficient action, also often demonstrates the same
fact by modifying or destroying the distinctness of the
second sound.

One reason for the second sound being a clearer and
sharper one than the first may be, that the semilunar
valves are not covered in by the thick layer of fibres

122 THE CIRCULATION. _

composing the walls of the heart to such an extent as are
the auriculo-ventricular. It might be expected therefore
that their vibration would be more easily heard through a
stethoscope applied to the walls of the chest.

The contraction of the auricles which takes place in the
end of the pause is inaudible outside the chest, but may be
heard, when the heart is exposed and the stethoscope
‘placed'.on it, as a slight sound preceding and continued
into the louder sound of the ventricular contraction.

The Impulse of the Heart.—At the commencement of
each ventricular contraction, the heart may be felt to beat
with a slight shock or impulse against the walls of the chest.
This impulse is most evident in the space between the fifth
and sixth ribs, between one and two inches to the left of
the sternum. The force of the impulse, and the extent to
which it may be perceived beyond this point, vary con-
siderably in different individuals, and in the same indi-
viduals under different circumstances. It is felt more
distinctly, and over a larger extent of surface, in emaciated
' than in fat and robust persons, and more during a forced
expiration than in a deep inspiration ; for, in the one case,
the intervention of a thick layer of fat or muscle between
the heart and the surface of the chest, and in the other the
inflation of the portion of lung which overlaps the heart,
prevents the impulse from being fully transmitted to the
surface. An excited action of the heart, and especially a
hypertrophied condition of the ventricles, will increase the
impulse, while a depressed condition, or an atrophied state
of the ventricular walls, will diminish it.

The impulse of the heart is probably the result, in part,
of a tilting forwards of the apex, so that it is made to
strike against the walls of the chest. This tilting move-
ment is thought to be effected by the contraction of the —
spiral muscular fibres of the ventricles, and especially of
certain of these fibres which, according to Dr. Reid, arise
from the base of the ventricular septum, pass downwards

IMPULSE OF THE HEART. 123

and forwards, forming part of the septum, then emerge
and curve spirally around the apex and adjacent portion
of the heart. The whole extent of the movement thus
produced is, however, but slight. The condition, which,
no doubt, contributes most to the occurrence and character
of the impulse of the heart, is its change of shape; for,
during the contraction of the ventricles, and the consequent
approximation of the base towards the apex, the heart
becomes more globular, and bulges so much, that a distinct
impulse is felt when the finger is placed over the bulging
portion, either at the front of the chest, or under the
diaphragm. The production of the impulse is, perhaps,
further assisted by the tendency of the aorta to straighten
itself and diminish its curvature when distended with the.
blood impelled by the ventricle; and by the elastic recoil
of all the parts about the base of the heart, which, accord-
ing to the experiments of Kurschner, are stretched down-
ward and backward by the blood flowing into the auricles
and ventricles during the dilatation of the latter, but re-
cover themselves when, at the beginning of the contraction
of the ventricles, the flow through the auriculo-ventricular
orifices is stopped. But these last-mentioned conditions
can only be accessory in the perfect state of things ; for the
same tilting movement of the heart ensues when its apex
is cut off, and when, therefore, no tension or change of
form can be produced by the blood.

Although what we generally recognise as the impulse of
the heart is produced in the way just mentioned, the beat
is not so simple a shock as it may seem when only felt
by the finger. By means of an instrument called a cardio-
graph, it may be shown to be compounded of three or four
shocks, of which the finger can only feel the greatest.

The cardiograph is a tube, dilated at one end into a
cup or funnel, either open-mouthed or closed by an elastic
membrane, while at the other it communicates with
the interior of a small metal drum, one side of which is

124 THE CIRCULATION,

formed by an elastic membrane, on which rests a finely-
balanced lever, like that of the sphygmograph (fig. 42).

When used, the cup at one end of the tube is placed
immediately over the part of the chest-wall at»which the
apex of the heart beats; while the lever on the drum is
placed in contact with a registering apparatus. (See de-
scription of sphygmograph, p. 147.) When the heart
beats, the shock communicates a series of impulses to the
column of air in the now closed tube, with the effect ot
raising the elastic wall of the drum, and of course the
lever which is attached to it. A tracing of the heart’s
impulse is thus obtained in the same way as that of the
pulse, in the arteries (figs. 44 and 45). .

The tracing shows that besides the strong beat which
alone the finger recognises as the impulse of the heart,
and which is caused by the contraction of the ventricles,
there are other minor shocks which are imperceptible to
the touch. The latter, M. Marey, by experiments on the
lower animals, has proved to be the results, respectively,
of the contraction of the auricles, and of the closure of the
auriculo-ventricular and semilunar valves.

Frequency and Force of the Heart’s Action.

The frequency with which the heart performs the actions
we have described, may be counted by the pulses at the
wrist, or in any other artery; for these correspond with
the contractions of the ventricles.

The heart of a healthy adult man in the middle period
of life, acts from seventy to seventy-five times in a minute.
The frequency of the heart’s action gradually diminishes
from the commencement to near the end of life, but is said
to rise again somewhat in extreme old age, thus :—

ACTION OF THE HEART. 125

In the embryothe average number of pulses in a minute is 150

Just after birth . : ; . ; . from 140 to 130
During the first year. ‘ ‘ ; , 130 to II5
During the second year. 3 F fe 115 to 100
During thethird year... ; ‘ ; 100 to 90
About the seventh year. , goto 85
About the fourteenth year, the sein fin bbe ‘

of pulses in a minute is from : ; <<. 3, OG 80 SO
Inadultage . , ; : : 2s OO 70
Inoldage . ‘ ; ; : : ; 70 to 60
In decrepitude . : ‘ ; ‘ Fe 75 to 65

In persons of sanguine temperament, the heart acts
somewhat more frequently than in those of the phleg-
matic; and in the female sex more frequently than in the
male.

After a meal its action is accelerated, and still more so
during bodily exertion or mental excitement; it is slower
during sleep. The effect of disease in producing temporary
increase or diminution of the heart’s action is well known.
From the observation of several experimenters, it appears
that, in the state of health, the pulse is most frequent in
the morning,.und becomes gradually slower as the day
advances: and that this diminution of frequency is both
more regular and more rapid in the evening than in the
morning. It is found, also, that as a general rule, the
pulse, especially in the adult male, is more frequent in the
standing than in the sitting posture, and in the latter than
in the recumbent position; the difference being greatest
between the standing and the sitting posture. The effect
of change of posture is greater as the frequency of the
pulse is greater, and, accordingly, is more marked in the
morning than in the evening. Dr. Guy, by supporting
the body in different postures, without the aid of muscular
effort of the individual, has proved that the increased
frequency of the pulse in the sitting and standing positions
is dependent upon the muscular exertion engaged in main-
taining them; the usual effect of these postures on the

126 THE CIRCULATION.

pulse being almost entirely prevented when the usually
attendant muscular exertion was rendered unnecessary.
The effect of food, like that of change of posture, is greater
in the morning than in the evening. According to Parrot,
the frequency of the pulse increases in a corresponding
ratio with the elevation above the sea; and Dr. Frankland
informed the author, that at the summit of Mont Blanc his
pulse was about double the ordinary standard all the time
he was there. After six hours’ perfect rest and sleep at
the top, it was 120, on descending to the corridor it fell to
108, at the Grands Mulets it was 88, at Chamounix 56;
normally, his pulse is 60.

In health there is observed a nearly uniform relation
between the frequency of the pulse and of the respirations;
the proportion being, on an average, one of the latter to
three or four of the former. The same relation is generally
maintained in the cases in which the pulse is naturally
accelerated, as after food or exercise; but in disease this
relation usually ceases to exist. In many affections accom-
panied with increased frequency of the pulse, the respira-
tion, is, indeed, also accelerated, yet the degree of its
acceleration bears no definite proportion to the increased
number of the heart’s actions: and in many other cases,
the pulse becomes more frequent without any accompany-
ing increase in the number of respirations; or, the respi-
ration alone may be accelerated, the number of pulsations
remaining stationary, or even falling below the ordinary
standard. (On the whole of this subject the article Pulse
by Dr. Guy, in the Cyclopzedia of Anatomy and Physiology,
may be advantageously consulted.)

.The force with which the left ventricle of the heart con-
tracts is about double that exerted by the contraction of
the right: being equal (according to Valentin) to about
=jth of the weight of the whole body, that of the right
being equal only to ;},th of the same. This difference

100
in the amount of force exerted by the contraction of the two

ACTION OF THE HEART. 127

ventricles, results from the walls of the left ventricle being
about twice as thick as those of the right. And the dif-
ference is adapted to the greater degree of resistance which
the left ventricle has to overcome, compared with that to
be overcome by the right: the former having to propel
blood through every part of the body, the latter only
through the lungs. |

The force exercised by the auricles in their contraction
has not been determined. Neither is it known with what
amount of force either the auricles or the ventricles dilate ;
but there is no evidence for the opinion, that in their dila-
tation they can materially assist the circulation by any such
action as that of a sucking-pump, or a caoutchouc bag, in
drawing blood into their cavities. That the force which
the ventricles exercise in dilatation is very slight, has been
proved by Oesterreicher. He removed the heart of a frog
from the body, and laid upon it a substance sufficiently
heavy to press it flat, and yet so small as not to conceal the
heart from view ; he then observed that during the con-
traction of the heart, the weight was raised; but that
during its dilatation, the heart remained flat. And the
same was shown by Dr. Clendinning, who, applying the
points of a pair of spring callipers to the heart of a live
ass, found that their points were separated as often as the
heart swelled up in the contraction of the ventricles, but
approached each other by the force of the spring when the
ventricles dilated. Seeing how slight the force exerted in
the dilatation of the ventricles is, it has been supposed
that they are only dilated by the pressure of the blood
impelled from the auricles; but that both ventricles and
auricles dilate spontaneously is proved by their continuing
their successive contractions and dilatations when the heart
is removed, or even when they are separated from one
another, and when therefore no such force as the pressure
of bloed can be exercised to dilate them. By such spon-
taneous dilatation they at least offer no resistance to the

128 THE CIRCULATION ;

influx of blood, and save the force which would otherwise
be required to dilate them.

The capacity of the two ventricles is probably exactly the
same. It is difficult to determine with certainty how much
this may be; but, taking the mean of various estimates,
it may be inferred that each ventricle is able to contain on
an average, about three ounces of blood, the whole of which
is impelled into their respective arteries at each contraction.
The capacity of the auricles is rather less than that of the
ventricles: the thickness of their walls is considerably less.
The latter condition is adapted to the small amount of
force which the auricles require in order to empty them-
selves into their adjoining ventricles; the former to the
circumstance of the ventricles being partly filled with blood
before the auricles contract.

Cause of the Rhythmic Action of the Heart.

It has been attempted in various ways to account for the
existence and continuance of the rhythmic movements of
the heart. By some it has been supposed that the contact
of blood with the lining membrane of the cavities of the
heart, furnishes a stimulus, in answer to which the walls
of these cavities contract. But the fact that the heart,
especially in Amphibia and fishes, will continue to contract
and dilate regularly and in rhythmic order after it is
removed from the body, completely emptied of blood, and
even placed in a vacuum where it cannot receive the
stimulus of the atmospheric air, is a proof that even if the
contact of blood be the ordinary stimulus to the heart’s
contraction, it cannot alone be an explanation of its
rhythmic motion,

The influence of the mind, and of some affections of the
brain and spinal cord upon the action of the heart, proves
that it is not altogether, or at all times, independent of
the cerebro-spinal nervous system. Yet the numerous
experiments instituted for the purpose of determining the

RHYTHM OF THE HEART. 129

exact relation in which the heart stands towards this
system, have failed to prove that the action is directly
governed under ordinary circumstances by the power of
any portion of the brain or spinal cord. Sudden destruc-
tion of either the brain or spinal cord alone, or of both
together, produces, immediately, a temporary interruption
or cessation of the heart’s action: but this appears to be
only an effect of the shock of so severe an injury; for, in
some such cases, ‘the movements of the heart are subse-
quently resumed, and if artificial respiration be kept up,
may continue for a considerable time; and may then again
be arrested by a violent shock applied through an injury
of the stomach. While, therefore, we must admit an
indirect or occasional influence exercised by, or through,
the brain and spinal cord upon the movements of the heart,
and may believe this influence to be the greater the more
highly the several organs are developed, yet it is clear that
we cannot ascribe the regular determination and direction
of the movements to these nervous centres. |

_The persistence of the movements of the heart in their
regular rhythmic order, after its removal from the body,
_and their capability of being then re-excited by an ordinary
stimulus after they have ceased, proved that the cause of
these movements must be resident within the heart itself.
And it seems probable, from the experiments and observa-
tions of various observers, that it is connected with the
existence of numerous minute ganglia of the sympathetic
nervous system, which, with connecting nerve-fibres, are
distributed through the substance of the heart. These
ganglia appear to act as so many centres or organs for the
production of motor impulses ; while the connecting nerve-
fibres unite them into one system, and enable them to act
in concert and direct their impulses so as to excite in
regular series the successive contractions of the several
muscles of the heart. The mode in which ganglia thus
act as centres and co-ordinators of nervous power will be

K

130 THE CIRCULATION.

described in the chapter on the Nervous System; and
it will appear probable that the chief peculiarity of the
heart, in this respect, is due to the number of its ganglia,
and the apparently equal power which they all exercise ;
so that there is no one part of the heart whose action, more
than another’s, determines the actions of the rest. Thus,
if the heart of a reptile be bisected, the rhythmic, suc-
cessive actions of auricle and ventricle will go on in both
halves: we therefore cannot say that the action of the
right side determines or regulates that of the left, or vice
versa; and we must suppose that when they act together
in the perfect heart, it is because they are both, as it were,
set to the same time. Neither can we say that the auricles
determine the action of the ventricles; for, if they are
separated, they will both contract and dilate in regular,
though not necessarily similar, succession. <A fact pointed
out by Mr. Malden shows how the several portions of each
cavity are similarly adjusted to act alike, yet independently
of each other. If a point of the surface of the ventricle
of a turtle’s or frog’s heart be irritated, it will immediately
contract, and very quickly afterwards all the rest of the
ventricle will contract; but, at the close of this general
contraction, the part that was irritated and contracted first,
is slightly distended or pouched out, showing that it was
adjusted to contract in, and for only, a certain time, and
that therefore as it began to contract first, so it began to
dilate first.

The best interpretation, perhaps, yet given of it, and
of rhythmic processes in general, is that by Mr. Paget,
who regards them as dependent on rhythmic nutrition, 7.c.,
on a method of nutrition in which the acting parts are
gradually raised, with time-regulated progress, to a certain
state of instability of composition, which then issues in the
discharge of their functions, ¢.g., of nerve-force in the case
of the cardiac ganglia, by which force the muscular walls
are excited to contraction. According to this view, there is

——————e—————oOwOroor

RHYTHM OF THE HEART. 131

in the nervous ganglia of the heart, and in all parts
originating rhythmic processes, the same alternation of
periods of action with periods of repose, during which the
waste in the structure is repaired, as is observed in most
of, if not all, the organic phenomena of life. All organic
processes seem to be regulated with exact observance of
time; and rhythmic nutrition and action, as exhibited in
the action of the heart, are but well-marked examples of
such chronometric arrangement,

We may conclude, then, that the nervous ganglia in
the heart’s substance are the immediate regulators of the
heart’s action, but that they are themselves liable to in-
fluences, conveyed from without, through branches of the
pneumogastric and sympathetic nerves.

The pneumogastric nerves are the media of an inhibitory
or restraining influence over the action of the heart; for
when by section their influence, is withdrawn, the pules-

tions of the organ are increased in frequency and d strength ; ;

while an opposite | effect i is produced by stimulating them
—the transmission of an electric current of pape ree
strength, diminishing the pulsations, or stopping them
altogether. Stimulation of the sympathetic nerves, on the
other hand, accelerates and st strengthens the heart’s action.
Various theories have been proposed to account for
these peculiar results, but none of them are very satis-
factory, and it is probable that many more facts must be
discovered before any theory on the subject can be per-

“manently maintained.

The connection of the action of the heart with the other
organs, and the influences to which it is subject through
them, are explicable from the connection of its nervous
system with the other ganglia of the sympathetic, and with
the brain and spinal cord through, chiefly, the pneumo-
gastric nerves. But this influence is proved in a much
more striking manner by the phenomena of disease than

by any experimental or. other physiological observations.
K 2

132 THE CIRCULATION,

The influence of a shock in arresting or modifying the
action of the heart,—its very slow action after compression
of the brain, or injury to the cervical portion of the spinal
cord,—its irregularities and palpitations in dyspepsia
and hysteria,—are better evidence for the connection of
the heart with the other organs through the nervous
system, than are any results obtained by experiments.

-

Effects of the Heart’s Action.

That the contractions of the heart supply alone a svffi-
cient force for the circulation of the blood, appears to be
established by the results of several experiments, of which
the following is one of the most conclusive:—Dr. Sharpey
injected bullock’s blood into the’ thoracic aorta of a dog
recently killed, after tying the abdominal aorta above the
renal arteries, and found that, with a force just equal to
that by which the ventricle commonly impels the blood in
the dog, the blood which he injected into the aorta passed
in a free stream out of the trunk of the vena cava inferior.
It thus traversed both the systemic and hepatic capillaries ;
and when the aorta was not tied above the renals, blood
injected under the same pressure flowed freely through the
vessels of the lower extremities. A pressure equal to that
of one and a half or two inches of mercury was, in the
same way, found sufficient to propel blood through the
vessels of the lungs.

But although it is probably true that the heart’s action
alone is sufficient to ensure the circulation, yet there exist
several other forces which are, as it were, supplementary ~
to the action of the heart, and assist it in maintaining the
circulation. The principal of these supplemental forces
have been already alluded to, and will now be more fully
pointed out.

;
‘
*
oF
|
*
=,
x
hy
oa
bi

—

- aCe

STRUCTURE OF ARTERIES. 133

THE ARTERIES,

_ The walls of the arteries are composed of three principal
coats, termed the external or tunica adventitia, the middle,
and the internal, while the latter is lined within by a single
layer of tesselated epithelium.

The external coat or tunica adventitia, the strongest and
toughest part of the wall of the artery, is formed of areolar
tissue, with which is mingled throughout a network of _
elastic fibres. At the inner part of this outer coat the
elastic network forms in most arteries so distinct a layer
as to be sometimes called the external elastic coat. pn

The middle coat is composed of both muscular and elastic
fibres. | .

The former, which are of the pale or unstriped variety (see
Chapter on Motion), are arranged Fig. 40.*
for the most part transversely to
the long axis of the artery; while
the elastic element, taking also
a transverse direction, is disposed
in the form of closely inter-
woven and branching fibres,
which intersect in all parts the
layers of muscular fibre. In
arteries of various size there is
a difference in the proportion of
the muscular and elastic element, /
elastic tissue preponderating in
the largest arteries, while this
condition is reversed in those of medium and small size.

The internal arterial coat is formed by layers of elastic
tissue, consisting in part of coarse longitudinal branching
fibres, and in part of a very thin and brittle membrane
which possesses little elasticity, and is thrown into folds

* Fig. 40. Muscular fibre-cells from human arteries, magnified 350
diameters (Kolliker). «a, natural state ; 0, treated with acetic acid.

134 THE CIRCULATION.

-

or wrinkles when the artery contracts. This latter mem-
brane, the striated or fenestrated coat of Henle, is pecu-
liar in its tendency to curl up, when peeled off from the
artery, and in the perforated and streaked appearance
which it presents under
the microscope. Its inner
surface is lined with a de-
licate layer of epithelium,
composed of thin squamous
elongated cells, which make
it smooth and polished, and
furnish a nearly imperme-
able surface, along which
the blood may flow with the
smallest possible amount of
resistance from friction.
The walls of the arteries, with the possible exception of
the epithelial lining and the layers of the internal coat
immediately outside it, are not nourished by the blood
which they convey, but are, like other parts of the body,
supplied with little arteries, ending in capillaries and veins,

which, branching throughout the external coat, extend for

some distance into the middle, but do not reach the internal
coat. These nutrient vessels are called vasa vasorum-.
Nerve-fibres are also supplied to the walls of the arteries.

The function of the arteries is to convey blood from the
heart to all parts of the body, and each tissue which enters
into the construction of an artery has a special purpose to
serve in this distribution.

(1.) The external coat forms a strong and tough invest-
ment, which, though capable of extension, appears prinei-
pally designed to strengthen the arteries 'and to guard
against their excessive distension from the force of the

* Fig. 41. Portion of fenestrated membrane from the crural artery,
magnified 200 diameters. a, 0, c, perforations (from Henle).

a. ee

fn 8 Be

EE I TE i

STRUCTURE OF ARTERIES. 135

heart’s action. In it, too, the little vasa vasorum find a
suitable tissue in which to subdivide for the supply of the
arterial coats.

(2.) The purpose of the elastic tissue, which enters so
largely into the formation of all the coats of the arteries, is,
ist, To guard the arteries from the suddenly exerted
pressure to which they are subjected at each contraction of
the ventricles. In every such contraction, the contents of
the ventricles are forced into the arteries more quickly
than they can be discharged into and through the capil-
laries.. The blood therefore being, for an instant, resisted
in its onward course, a part of the force with which it was
impelled is directed against the sides of the arteries; under
this force, which might burst a brittle tube, their elastic
walls dilate, stretching enough to receive the blood, and
as they stretch, becoming more tense and more resisting.
Thus, by yielding, they, as it were, break the shock of the
force impelling the blood, and exhaust it before they are

in danger of bursting, through being overstretched. Elas-

ticity is thus advantageous in all arteries, but chiefly so in
the aorta and its large branches, which are provided, as
already said, with a large proportional quantity of elastic
tissue, in adaptation to the great force of the left ventricle,
which falls first on them, and to the increased pressure of
the arterial blood in violent expiratory efforts.

On the subsidence of the pressure, when the ventricles
cease contracting, the arteries are able, by the same elas-
ticity, toresume their former calibre; and in thus doing,
they manifest the 2nd chief purpose of their elasticity, that,
namely, of equalizing the current of the blood by main-
taining pressure on the blood in the arteries during the
periods at which the ventricles are at rest or dilating. If
some such method as this had not been adopted—if for
example the arteries had been rigid tubes, the blood,
instead of flowing, as it does, in a constant stream, would
have been propelled through the arterial system in a series

136 THE CIRCULATION.

of jerks corresponding to the ventricular contractions, with
intervals of almost complete rest during the inaction of the
ventricles. But in the actual condition of the arteries, the
force of the successive contractions of the ventricles is
expended partly in the direct propulsion of the blood, and
partly in the dilatation of the elastic arteries; and in the
intervals between the contractions of the ventricles, the
force of the recoiling and contracting arteries is employed
in continuing the same direct propulsion. Of course, the
pressure exercised by the recoiling arteries is equally
diffused in every direction through-the blood, and th

blood would tend to move backwards as well as onwards
but that all movement backwards is prevented by the
closure of the semi-lunar arterial valves, which takes place
at the very commencement of the recoil of the arterial
walls. :

By this exercise of the elasticity of the arteries, all the
force of the ventricles is made advantageous to the circula-
tion; for that part of their force which is expended in
dilating the arteries, is restored in full, according to that
law of action of elastic bodies, by which they return to the
state of rest with a force equal to that by which they were
disturbed therefrom. There is thus no loss of force; but
neither is there any gain, for the elastic walls of the artery
cannot originate any force for the propulsion of the blood—
they only restore that which they received from the ventri-
cles; they would not contract had they -not first been
dilated, any more than a spiral spring would shorten itself
unless it were first elongated. The advantage of elasticity
in this respect is, therefore, not that it increases, but that
it equalizes or diffuses the force derived from the periodic
contractions of the ventricles. The force with which the
arteries are ‘dilated every time the ventricles contract,
might be said to be received by them in store, to be all
given out again in the next succeeding period of dilatation
of the ventricles. It is by this equalizing influence of the

ELASTICITY OF ARTERIES. 137

successive branches of every artery that, at length, the
intermittent accelerations produced in the arterial current
by the action of the heart, cease to be observable, and the
jetting stream is converted into the continuous and equable
movement of the blood which we see in the capillaries and
veins. .

In the production of a continuous stream of blood in the
smaller arteries and capillaries, the resistance which is
offered to the blood-stream in the capillaries (p. 161) is a
necessary agent. Were there no greater obstacle to the
escape of blood from the arteries than exists to its entrance
into them from the heart, the stream would be intermittent,
‘notwithstanding the elasticity of the walls of the arteries.

It is the resistance which the left ventricle meets with
in forcing blood into the arteries that causes part of the
force of its contraction to be expended in dilating them,
or, as before remarked, in laying up in them a power
which will act in the intervals of the ventricle’s contrac-
tion.

(3.) By means of the elastic tissue in their walls (and of
the muscular tissue also), the arteries are enabled to dilate
and contract readily in correspondence with any temporary
increase or diminution of the total quantity of blood in
the body; and within a certain range of diminution of
the quantity, still to exercise due pressure on their
contents.

The elastic coat, however, not only assists in restoring
the normal calibre of an artery after temporary dilatation,
but also (4) may assist in restoring it after diminution of
the calibre, whether this be caused by a temporary con-
traction of the muscular coat, or the application of a com-
pressing force from without. This action of the elastic
tissue in arteries, is well shown in arteries which contract
after death, but regain their average patency on the cessa-
tion of post-mortem rigidity (p. 140). (5.) By means of
their elastic.coat the arteries are enabled to adapt them-

138 THE CIRCULATION.

selves to the different movements of the several parts of
the body.

We have already referred to the fact that the middle
coat of the arteries is composed of unstriped muscular
fibres, mingled with fine elastic filaments. The evidence
for the muscular contractility of arteries may, however, be
given briefly for the sake of the physiological facts on
which it hinges.

(1.) When a small artery in the living subject is exposed
to the air or cold, it gradually but manifestly contraets.
Hunter observed that the posterior tibial artery of a dog,
when laid bare, became in a short time so much contracted
as almost to prevent the transmission of blood; and the
observation has been often and variously confirmed.
Simple elasticity could not effect this; for after death,
- when the vital muscular power has ceased, and the
mechanical: elastic one alone operates, the contracted
artery dilates again.

(2.) When an artery is cut across, its divided ends con-
tract, and the orifices may be completely closed. The
rapidity and completeness of this contraction vary in
different animals; they are generally greater in young
than in old animals; and less, apparently, in man than in
animals. In part this contraction is due to elasticity, but
in part, no doubt, to muscular action; for it is generally
increased by the application of cold, or of any simple
stimulating substances, or by mechanically irritating the
cut ends of the artery, as by picking or twisting them.
Such irritation would not be followed by these effects, if
the arteries had no other power of contracting than that
depending upon elasticity.

(3.) The contractile property of arteries continues many
hours after death, and thus affords an opportunity of dis-
tinguishing it from elasticity. When a portion of an artery,
the splenic, for example, of a recently killed animal, is
exposed, it gradually contracts, and its canal may be

MUSOULARITY OF ARTERIES. © 139

thus completely closed: in this contracted state it remains
for a time, varying from a few hours to two days: then it
dilates again, and permanently retains the same size. If,
while contracted, the artery be forcibly distended, its con-
tractility is destroyed, and it holds a middle or natural size.

This persistence of the contractile property after death
was well shown in an observation of Hunter, which may
be mentioned as proving, also, the greater degree of
contractility possessed by the smaller than by the larger
arteries. Having injected the uterus of a cow, which had
been removed from the animal upwards of twenty-four
hours, he found, after the lapse of another day, that the
larger vessels had become much more turgid than when he
injected them, and that the smaller arteries had contracted
so as to force the injection back into the larger ones.

The results of an experiment which Hunter made with
the vessels of an umbilical cord prove still more strikingly
the long continuance of the contractile power of arteries
after death. In a woman delivered on a Thursday after-
noon, the umbilical cord was separated from the foetus,
having been first tied in two places, and then cut between,
so that the blood contained in the cord and placenta was
confined in them, On the following morning, Hunter tied
a string round the cord, about an inch below the other
ligature, that the blood might still be confined in the
placenta and remaining cord. Having cut off this piece,
and allowed all the blood to escape from its vessels, he
attentively observed to what size the ends of the cut arte-
ries were brought by the elasticity of their coats, and then
laid aside the piece of cord to see the influence of the
contractile power of its vessels. On Saturday morning,
the day after, the mouths of the arteries were completely
closed up. He repeated the experiment the same day with
another portion of the same cord, and on the following
morning found the results to be precisely similar. On the
Sunday he performed the experiment the third time, but

140 y THE CIRCULATION.

the artery then seemed to have lost its contractility, for on
the Monday morning, the mouths of the cut arteries were
found open. In each of these experiments there was but
little alteration perceived in the orifices of the veins.

(4.) The influence of cold in increasing the contraction of
a divided artery has been referred to: it has been shown,
_ also, by Schwann, in an experiment on the mesentery of a
living toad. Having extended the mesenter under the
microscope, he placed upon it a few drops of water, the
temperature of which was some degrees lower than that of
the atmosphere. The contraction of. the vessels soon com-
menced, and gradually increased until, at the expiration of
ten or fifteen minutes, the diameter of the canal of an
artery, which at first was 0°0724 of an English line, was
reduced to 0'0276. ‘The arteries then dilated again, and
at the expiration of half an hour had acquired nearly their
original size. By renewing the application of the water,
the contraction was reproduced: in this way the experi-
ment could be performed several times on the-same artery.
It is thus proved, that cold will excite contraction in the .
walls of very small, as well as of comparatively large
arteries: it could not produce such contraction in a merely
elastic substance; but it'is a stimulus to the organic mus-
cular fibres in many other parts, as well as in the arterial
coat ; as, ¢.g., in the skin, the dartos, and the walls of the
bronchi.

(5.) Lastly, satisfactory evidence of the muscularity of
the arterial coats is furnished by the experiments of Ed.
and E. H. Weber, and of Professor Kélliker, in which
they applied the stimulus of electro-magnetism to small
arteries. The experiments of the Webers were performed
on the .small mesenteric arteries of frogs; and the most
striking results were obtained when the diameter of the
vessels examined did not exceed from + to 5}, of a Paris
line. When a vessel of this size was exposed to the elec-
tric current, its diameter in from five to ten seconds, became

FUNCTIONS OF MUSCULAR COAT. I4t

one-third less, and the area of its section about one-half.
On continuing the stimulus, the narrowing gradually in-
creased, until the calibre of the tube became from three to
six times smaller than it was at first, so that only a single
row of blood-corpuscles could pass along it at once; and
eventually the vessel was closed and the current of blood
arrested. |

With regard to the purpose served by the muscular coat of
the arteries, there appears no sufficient reason for supposing .
that it assists, to more than a very small degree, in pro-
pelling the onward current of blood. Its most important
office is that of regulating the quantity of blood to be
received by each part, and of adjusting it to the require-
ments of each, according to various circumstances, but

_ chiefly and most naturally, according to the activity with

which the functions of each part are at different times per-
formed. The amount of work done by each organ of the
body varies at different times, and the variations often
quickly succeed each other, so that, as in the. brain for
example, during sleep and waking, within the same hour
a part may be now very active and then inactive. In all
its active exercise of function, such a part requires a larger
supply of blood than is sufficient for it during the times
when it is comparatively inactive. It is evident that the
heart cannot regulate the supply to each part at different
periods, neither could this be regulated by any general
and uniform contraction of the arteries; but it may be
regulated by the power which the arteries of each part
have, in their muscular tissue, of contracting so as to
diminish, and of passively dilating or yielding so as to
permit an increase of, the supply of blood, according as
the requirements of the part may demand. And thus,
while the ventricles of the heart determine the total
quantity of blood, to be sent onwards at each contraction,
and the force of its propulsion, and while the large and
merely elastic arteries distribute it and equalise its stream,

142 THE CIRCULATION.

the smaller arteries with muscular tissue add to these two
purposes, that of regulating and determining, according to
its requirements, the proportion of the whole quantity of
blood which shall be distributed to each part.

It must be remembered, however, that this regulating
function of the arteries is itself governed and directed by
the nervous system.

The muscular tissue of arteries is supplied with nerves
chiefly, if not entirely, by branches from the sympathetic
system. These so-called vaso-motor nerves are again con-
nected, through the medium of ganglia, with the fibres
from the sympathetic system supplied to the organs
nourished by these same arteries. Thus, any condition in
these organs which causes them to need a different amount
of blood, whether more or less, produces a certain im-
pression on their nerves, and by these the impression is
carried to the ganglia, and thence reflected along the
nerves which supply the arteries. The muscular element
of these vessels responds in obedience to the impression
conveyed to it by the nerves; and, according to its contrac-
tion or dilatation, is a larger or smaller quantity of blood
allowed to pass. )

Another function of the muscular element of the middle
coat of arteries is, doubtless, to co-operate with the elastic
in adapting the calibre of the vessels to the quantity of
blood which they contain. For the amount of fluid in the
blood-vessels varies very considerably even from hour to
hour, and can never be quite constant, and were the elastic
tissue only present, the pressure exercised by the walls of
the containing vessels on the contained blood would be
sometimes very small, and sometimes inordinately great.
The presence of a muscular element, however, provides
for a certain uniformity in the amount of pressure exer-
cised ; and it is by this adaptive, uniform, gentle, muscular,
contraction, that the tone of the blood-vessels is maintained.
Deficiency of this tone is the cause of the soft and yield-

es * —— -

ee Be,

THE PULSE. 143

ing pulse, and its unnatural excess of the hard and tense
one.

The elastic and muscular contraction of an artery may
also be regarded as fulfilling a natural purpose when, the
artery being cut, it first limits and then, in conjunction
with the coagulated fibrin, arrests the escape of blood. It
is only in consequence of such contraction and coagulation
that we are free from danger through even very slight
wounds; for it is only when the artery is closed that the
processes for the more permanent and secure prevention of
bleeding are established.

Mr. Savory has shown that the natural state of all arte-
ries, in regard at least to their length, is one of tension—
that they are always more or less stretched, and ever ready
to recoil by virtue of their elasticity, whenever the oppos-
ing force is removed. The extent to which the divided
extremities of arteries retract is a measure of this tension,
not of their elasticity.

_ From what has been said in the preceding pages, it |
appears that the office of the arteries in the circulation is,—
1st, the conveyance and distribution of blood to the several
parts of the body; 2nd, the equalization of the current, and
the conversion of the pulsatile jetting movement given to.
the blood by the ventricles, into an uniform flow; 3rd, the
regulation of the supply of blood to each part, in accord-
ance with its demands.

The Pulse.

The jetting movement of the blood, which, as just stated,
it is one of the offices of the arteries to change into an uni-
form motion, is the cause of the pulse, and therefore needs
a separate consideration. We have already said, that as the
blood is not able to pass through the arteries so quickly as
it is forced into them by the ventricle, on account of the
resistance it experiences in the capillaries, a part of the

144 THE CIRCULATION.

force with which the heart impels the blood is exercised
upon the walls of the vessels which it distends. The
distension of each artery increases both its length and its
diameter. In their elongation, the arteries change their
form, the straight ones becoming curved, or having such a
tendency, and those already curved becoming more so; *
but they recover their previous form as well as their dia-
meter when the ventricular contraction ceases, and their
elastic walls recoil. The increase of their curves which
accompanies the distension of arteries, and the succeeding
recoil, may be well seen in the prominent temporai artery
of an old person. The elongation of the artery is in such
a case quite manifest.

The dilatation or increase of the diameter of the artery
is less evident. In several reptiles, it may be seen without
aid, in the immediate vicinity of the heart, and it may be

watched, with a simple magnifying glass, in the aorta of

the tadpole. Its slight amount in the smaller arteries, the

difficulty of observing it in opaque parts, and the rapidity |

with which it takes place, are sufficient to account for its
being, in Mammalia, imperceptible to the eye. But in
these also experiment has proved its occurrence. Flourens,
in evidence of such dilatation, says he encircled a large
artery with a thin elastic metallic ring cleft at one point,
and that at the moment of pulsation the cleft part became
perceptibly widened. |
This dilatation of an artery, and the elongation producing
curvature, or increasing the natural curves, are sensible to
the finger placed over the vessel, and produce the pulse.
The mind cannot distinguish the sensation produced by
the dilatation from that produced by the elongation and

* There is, perhaps, an exception to this in the case of the aorta, of
which the curve is by some supposed to be diminished when it is elon-
gated; but if this be so, it is because only one end of the arch is im-
moveable ; the other end, with the heart, may move forward slightly
when the ventricles contract.

ee eee

— ‘
, ="

pawer gi, Or
jo

THE PULSE. 145

curving ; that which it perceives most plainly, however, is
the dilatation.*

The pulse—due to any given beat of the heart—is not
perceptible at the same moment in all the arteries of the

‘body. ‘Thus it can be felt in the carotid a very short time

before it is perceptible in the radial artery, and in this
vessel again before the dorsal artery of the foot. The
delay in the beat is in proportion to the distance of the
artery from the heart, but the difference in time between

* For this fact, which is contrary to the commonly accepted doctrine,
I am indebted to my friend, Dr. Hensley, who has kindly furnished me
with the following note on the subject :— |

By determining the conditions of equilibrium of a portion of artery
supposed cylindrical and filled with blood at a given pressure, it is easily
shown that the transverse tension is double the longitudinal.

Also it may be shown experimentally that, if strips of equal breadth,
cut in the two directions from one of the larger arteries, be stretched by
equal weights, the stretching of the transverse slip is somewhat greater
than that of the longitudinal one.

(By the word stretching is to be understood amount of stretching, and
jot increase of length :—it may be measured by the ratio which the
increase of length bears to the original length :—Thus things whose
natural lengths are 5 and 10 inches are equally stretched when their
lengths are made 6 and 12 inches respectively.)

Such experiments also show that, within certain limits, the stretching
of each strip varies directly as its tension.

Hence it will be seen that the transverse stretching of an artery, when
filled with blood, must be somewhat more than double its Sct i a
, stretching.

This being true for different blood pressures, the difference bet frees
the transverse stretchings for different pressures must be somewhat more
than double the difference between the corresponding longitudinal
stretchings ; and thus we can hardly be justified in saying that the
increase of longitudinal stretching which takes place with the pulse is
greater than the increase of transverse stretching.

It must also be remembered that the arteries are, under all circum-
stances, naturally in a state of tension longitudinally, and that their
length, therefore, cannot be increased at all until the blood pressure is
increased beyond a certain point.—(Eb. )

L

146 THE CIRCULATION.

the beat of any two arteries never exceeds probably 4 to }
of a second.

A great deal of light has been thrown on what may
be called the form of the pulse by the sphygmograph (figs.
42 and 43). The principle on which the sphygmograph
acts is very simple (see fig. 42). The small button re-
places the finger in the ordinary act of taking the pulse,
and is made to rest lightly on the artery, the pulsations of
which it is desired to investigate. The up-and-down
movement of the button is communicated to the lever. to
the hinder end of which is attached a slight spring, which
allows the lever to move up, at the same time that it is

Fig. 42.*

a

At tas eects Tie eee pees SPRING

just strong enough to resist its making any sudden jerk,
and in the interval of the beats also to assist in bringing it

* Fig. 42. Diagram of the mode of action of the Sphygmograph.
} Fig. 43. The Sphygmograph applied to the arm.

PULSE-TRACINGS. 147

back to its original position. For ordinary purposes, the
instrument is bound on the wrist (fig. 43).

It is evident that the beating of the pulse with the
reaction of the spring will cause an up-and-down move-
ment of the lever, and if the extremity of the latter be
inked, it will write the effect on the card, which is made
¢o move by clockwork in the direction of the arrow. Thus
a tracing of the pulse is obtained, and in this way much
more delicate effects can be seen, than can be felt on the
application of the finger.

Fig. 44 represents a healthy pulse-tracing of the radial
artery, but somewhat deficient in tone. On examination,
we see that the up-stroke which represents tlie beat of the
pulse is a nearly vertical line, while the down-stroke is

Fig. 44.*

very slanting, and interrupted by a slight re-ascent. ‘The
more vigorous the pulse, if it be healthy, theless is this
re-ascent, and vice versd. Fig. 45 represents the tracing

* Fig. 44. Pulse-tracing of radial artery, somewhat deficient in éone.
7 Fig. 45. Firm and long pulse of vigorous health.
t Fig. 46. Pulse-tracing of radial artery, with double apex.
The above tracings are taken from Dr. Sanderson’s work ‘‘ On the
Sphygmograph.”
L 2

148 é THE CIRCULATION,

of a healthy pulse in which the tone of the vessel is better
than in the last instance, and the down-stroke is therefore
less interrupted.

Sometimes the up-stroke has a double apex, as in fig.
46. This will be explained hereafter.

Before proceeding to consider the formation of the wale
as shown by these tracings, it is necessary to consider what
are the elements combined to produce it.

The heart at regular intervals discharges a certain
quantity of blood into the arteries and their branches,
already filled, though not distended to the utmost, with
fluid. This fresh quantity of blood obtains entrance by
the yielding of the artery’s elastic walls, and, on the
cessation of the propelling force, and when these walls
recoil, the blood is prevented from returning into the
ventricle whence it is issued, by the shutting of the semi-
lunar valves in the manner before described (p. 117). The
pressure, therefore, which is exercised on the blood by the
contracting arterial walls, will cause it to travel in a direc-
tion away from the heart, or, in other words, towards the
capillaries and veins.

It was formerly supposed that the pulse was caused -not
by the direct action of the ventricle, but by the propaga-
tion of a wave in consequence of the elastic recoil of the
large arteries, after their distension; and successive acts of .
dilatation and recoil, extending along the arteries in the
direction of the circulation, were, supposed to account for
the later appearance of the pulse in the vessels most ~
distant from the heart. The fact, however, that the pulse
is perceptible in every part of the arterial system previous
to the occurrence of the second sound of the heart, that is,
previous to the closure of the aortic valves, is a fatal
objection to this theory. For, if the pulse were the effect
of a wave propagated by the alternate dilatation and con-
traction of successive portions of the arterial tube, it ought,
in all the arteries except those nearest to the heart, to

i °

PULSE-TRACINGS. 149

follow or coincide with, but could never precede, the second
sound of the heart; for the first effect of the elastic recoil
of the arteries first dilated is the closure of the aortic
valves; and their closure produces the second sound.

The theory which seems to reconcile all the facts of the
case, and especially those two which appear most opposed,
namely, that the pulse always precedes the second sound
of the heart, and yet is later in the arteries far from the
heart than in those near it, may be thus stated :—It sup-
poses that the blood which is impelled onwards by the left
ventricle does not so impart its pressure to that which the
arteries already contain, as to dilate the whole arterial
system at once; but that it enters the arteries, it displaces
and propels that which they before contained, and flows on
with what may be called a head-wave, like that which is
formed when a rapid stream of water overtakes another
moving more slowly. The slower stream offers resistance
to the more rapid one, till their velocities are equalized:
and, because of such resistance, some of the force of the
more rapid stream of blood just expelled from the ventricle,
is diverted laterally, and with the rising of the wave the
arteries nearest the heart are dilated and elongated. They
do not at once recoil, but continue to be distended so long
as blood is entering them from the ventricle. The wave
at the head of the more rapid stream of blood runs on,
propelled and maintained in its velocity by the continuous
contraction of the ventricle: and it thus dilates in succes-
sion every portion of the arterial system, and produces the
pulse in all. At length, the whole arterial system (where-
in a pulse can be felt) is dilated; and at this time, when
the wave we have supposed has reached all the smaller
arteries, the entire system may be said to be simulta-
neously dilated; then it begins to contract, and the con-
tractions of its several parts ensue in the same succession
as the dilatations, commencing at the heart. The contrac-
tion of the first portion produces the closure of the valves

150 THE CIRCULATION,

and the second sound of the heart; and both it and the
progressive contractions of all the more distant parts main-
tain, as already said, that pressure on the blood during
the inaction of the ventricle, by which the stream of the
arterial blood is sustained between the jets, and is finally
equalized by the time it reaches the capillaries.

It may seem an objection to this theory, that it would
probably require a larger quantity of blood to dilate all
the arteries than can be discharged by the ventricle at each
contraction. But the quantity necessary for such a pur-
pose is less than might be supposed. Injections of the
arteries prove that, including all down to those of about
one-eighth of a line in diameter, they do not contain on
an average more than one and a half pints of fluid, even
when distended. There can be no doubt, therefore, that
the three or four ounces which the ventricle is supposed
to discharge at each contraction, being added to that
which already fills the arteries, would be sufficient to
distend them all. ,

A distinction must be carefully made between the passage
of the wave along the arteries, and the velocity of the stream
(p. 155) of blood. Both wave and current are present; but
the rates at which they travel are very different, that of the
wave being twenty or thirty times as great as that of the
current.

Returning now to the consideration of the pulse-tracings
(p. 147), it may be remarked that, in each, the up-stroke
corresponds with the period during which the ventricle is
contracting; the down-stroke, with the interval between
its contractions, or in other words with the recoil, after
distension, of the elastic arteries. In the large arteries,
when at least there is much loss of tone, the up-stroke is
double, the almost instantaneous propagation of the force
of contraction of the left ventricle along the column of
blood in the arteries, or the percussion-impulse, as it
is termed by Dr. Sanderson, being sufficiently strong to

a

PULSE-TRACINGS. I5I

jerk up the lever for an instant, while the wave of blood,
rather more slowly propagated from the ventricle, catches
it, so to speak, as it begins to fall, and again slightly
raises it.

In the radial artery tracings, on the other hand, we see
that the up-stroke is single. In this case the percussion:
impulse is not sufficiently strong to jerk up the lever and
produce an effect distinct from that of the systolic wave
which immediately follows it, and which continues and
completes the distension. In cases of feeble arterial
tension, however, the percussion-impulse may be traced
by the sphygmograph, not only in the carotid pulse, but
to a less extent in the radial also (fig. 46).

In looking now at the down-stroke (fig. 44) in the
tracings, we see that in the case of an artery with defi-
cient tone, it is interrupted by a well-marked notch, or, in
other words, that the descent is interrupted by a slight

uprising. There are indications also of slighter irregu-

larities or vibrations during the fall of the lever; while
these are alone to be seen in the pulse of heaith, or, in
other wordsy when the walls of the artery are of good
tone (fig. 45). In some cases of disease the re-ascent is
so considerable as to be perceptible to the finger, and this
double beat has received the technical name of ‘‘dicrotous”’
pulse. As a diseased condition this has long been recog-
nized, but it is only since the invention of the sphygmo-
graph that it has been found to belong in a certain degree
to the normal pulse also.

Various theories have been framed to account for the
dicrotism of the pulse. By some, it is supposed to be due
to the aortic valves, the sudden closure of which stops the
incipient regurgitation of blood into the ventricle, and
causes a momentary rebound throughout the arterial
system; while Dr. Sanderson considers it to be caused by
a kind of rebound from the periphery rather than from
the central part of the circulating apparatus.

152 THE CIRCULATION.

as Force of the Blood in the Arteries.

The force with which the ventricles act in their con-
traction, and the reasons for believing it sufficient for the
circulation of the blood, have been already mentioned.
Both calculation and experiment have proved, that very
little of this force is consumed in the arteries. Dr. Thomas

Fig. 47. Young calculated that the loss of
force in overcoming friction and other
hindrances in the arteries would be so
slight, that if one tube were introduced
into the aorta, and another into any
other artery, even into one as fine as
hair, the blood would rise in the tube
from the small vessel to within two
inches of the height to which it would
rise from the large vessel. The cor-
rectness of the calculation is esta-
blished by the experiments of Poi-
seuille, who invented an instrument
named a hemadynamometer, for es+
timating the statical pressuré>exer-
cised by the blood upon the walls of
the arteries. It consists of a long
glass tube, bent so as to have a short
horizontal portion (fig. 47), a branch
(2) descending at right angles from it,
and a long ascending branch (3).
Mercury poured into the ascending
and descending portions, will necessarily have the same
level in both branches, and in a vertical position the
height of its column must be the same in both. If, now,
the blood is made to flow from an artery, through the
horizontal portion of the tube (which should contain a
solution of carbonate of potash to prevent coagulation)
into the descending branch, it will exert on the mercury a

¥

ih bea Fats ade

eT G8 ia al GF a

TY

V-fs toy ‘

FORCE OF BLOOD IN ARTERIES. 153

pressure equal to the force by which it is moved in the
arteries; and the mercury will, in consequence, descend in
this branch, and ascend in the other. The depth to which
it sinks in the one branch, added to the height to which it
rises in the other, will give the whole height of the column
of mercury which balances the pressure exerted by the
blood; the weight of the blood, which takes the place of
the mercury in the descending branch, and which is more
than ten times less than the same quantity of quicksilver,
being subtracted. Poiseuille thus calculated the force
with which the blood moves in an artery, according to the
laws of hydrostatics, from the diameter of the artery, and
the height,of the column of’ quicksilver; that is to say,
from the weight of a column of mercury, whose base is a
circle of the same diameter as the artery, and whose height
is equal to the difference in the levels of the mercury in
the two branches of the instrument. He found the blood’s
pressure equal in all the arteries examined; difference in
size, and distance from the heart being unattended by any
corresponding difference of force in the circulation. The
height of the «column of mercury displaced by the blood

was the same in all the arteries of the same animal. The

correctness of these views having been questioned, Poi-
seuille has recently repeated his observations, and obtained
the same results.

From the mean result of several observations on horses
and dogs, the calculated that the force with which the
blood is moved in any large artery, is capable of support- |
ing a column of mercury six inches and one and a half.
lines in height, or a column of water seven feet one line in
height. With these results, the more recent observations —
of other experimenters closely accord. Poiseuille’s experi-
ments having thus shown to him that the force of the
blood’s motion is the same in the most different arteries,
he concluded that, to measure the amount of the blood’s
pressure in any artery of which the calibre is known, it is

a —-

154 THE CIRCULATION.

necessary merely to multiply the area of a transverse sec-
tion of a vessel by the height of the column of mercury
which is already known to be supported by the force of
the blood in any part of the arterial system. The weight
of a column of mercury of the dimensions thus found, will
represent the pressure exerted by the column of blood.
And assuming that the mean of the greatest and least
height of the column of mercury found, by experiments
on different animals, to be supported by the force of the
blood in them, is equivalent to the height of the column
which the force of the blood in the human aorta would
support, he calculated that about 4 lbs. 4 oz. avoirdupois
would indicate the static force with which the blood is
impelled into the human aorta. By the same calculation,

he estimated the force of the circulation in the aorta of the |

mare to be about 11 lbs. 9 oz. avoirdupois: and that in the
radial artery at the human wrist only 4 drs. We have
already seen that the muscular force of the right ventricle

is equal to only one half that of the left, consequently, if

- Poiseuille’s estimate of the latter be correct, the force with

which the blood is propelled into the lungs will only be
equal to 2 lbs. 2 oz. avoirdupois.

The amounts above stated indicate the pressure exerted
by the blood at the several parts of the arterial system at

the time of the ventricular contraction. During the dila-

tation, this pressure is somewhat diminished. MHales
observed, that the column of blood in the ttibe inserted
into an artery, falls an inch, or rather more, after each
pulse; Ludwig has observed the same, and recorded it
more minutely. The pressure is also influenced by the
various circumstances which affect the action of the heart;
the diminution or increase of the pressure being pro-
portioned to the weaker or stronger action of this organ.
Valentin observed that, on increasing the amount of
blood by the injection of a fresh quantity into it, the
pressure in the vessels was also increased, while a
, 4 ft

\ ; : " .
mis Al;

Ko iry frag , 1G —-Wi ow i Lay,
’ | .

VELOCITY OF BLOOD IN ARTERIES. 155

contrary effect ensued on diminishing the quantity of
blood.
Velocity of the Blood in the Arteries.

The velocity of the stream of blood is greater in the
arteries than in any other part of the circulatory system,
and in them it is greatest in the neighbourhood of the
heart, and during the ventricular systole; the rate of
movement diminishing during the diastole of the ven-
tricles, and in the parts of the arterial system most distant
‘from the heart. From Volkmann’s experiments with the
hemodromometer, it may be concluded that the blood
moves in the large arteries near the heart at the rate of |
about ten or twelve inches per second. Vierordt calculated —
the rapidity of the stream at about the same rate in the
arteries near the heart, and at two and a quarter inches
per second in the arteries of the foot.

THE CAPILLARIES.

In all organic textures, except some parts of the corpora
cavernosa of the penis, and of the uterine placenta, and of
the spleen, the transmission of the blood from the minute
branches of the arteries to the minute veins is effected
through a network of microscopic vessels, in the meshes
of which the proper substance of the tissue lies (fig. 48).
This may be seen in all minutely injected preparations;
and during life, by the aid of the microscope, in any trans-
parent vascular parts,—such as the web of the frog’s foot,
the tail or external branchie of the tadpole, or the wing
of the bat.

‘The ramifications of the minute arteries form repeated
anastomoses with each other and give off the capillaries
which, by their anastomoses, compose a continuous and
uniform network, from which the venous radicles, on the
other hand, take their rise. The reticulated vessels con-
necting the arteries and veins are called capillary, on

156 THE CIRCULATION.

account of their minute size; and intermediate vessels, on
account of their position. The point at which the arteries
terminate and the minute veins
commence, cannot be exactly de-
fined, for the transition is gradual;
butthe intermediate network has,
nevertheless, this peculiarity, that
the small vessels which compose
it maintain the same diameter
throughout; they do not diminish
in diameter in one direction, like
arteries and veins; and the
meshes of the network that they
compose are more uniform in
shape and size than those formed
by the anastomoses of the minute
arteries and veins.

The structure of the capillaries
is much more simple than that of
the arteries or veins. Their walls
are composed of a single layer of elongated or radiate,
flattened and nucleated cells, so joined and dovetailed
together as to form a continuous transparent membrane
(fig. 49). Outside these cells, in the larger capillaries,
there is a structureless, or very finely fibrillated membrane,
on the inner surface of which they are laid down.

The diameter of the capillary vessels varies somewhat in
the different textures of the body, the most common size
being about ;,)5;th of an inch. Among the smallest may
be mentioned those of the brain, and of. the follicles
of the mucous membrane of the intestines; among the

Fig. 48.*

* Fig. 48. Blood-vessels of an intestinal villus, representing the
arrangement of capillaries between the ultimate venous and arterial
branches ; a, a, the arteries ; 0, the vein.

a

a

THE CAPILLARIES. © 157

largest, those of the skin, and especially those of the
medulla of bones.

The form of the capillary network presents considerable
variety in the different textures of the body: the varieties

Fig 49.*

consisting principally of modifications of two chief kinds
of mesh, the rounded and the elongated. That kind in
which the meshes or interspaces have a roundish form is
the most common, and prevails in those parts in which the
capillary network is most dense, such as the lungs (fig. 50),

* Fig. 49. Magnified view of capillary vessels from the bladder of
the cat.—A, V, an artery and a vein; ¢, transitional vessel between
them and ¢, c, the capillaries. The muscular coat of the larger vessels
is left out in the figure to allow the epithelium to be seen: at ¢c, a
radiate epithelium scale with four pointed processes, running out upon
the four adjoining capillaries (after Chrzonszczewesky, Virch. Arch.
1866). i ;

158 THE CIRCULATION

most glands, and mucous membranes, and the cutis. The
meshes of this kind of network are not quite circular,
but more or less angular, sometimes presenting a nearly
regular quadrangular or polygonal form, but being more
frequently irregular. The capillary network with elon-
gated meshes (fig. 51) is observed in parts in which the

Fig. 50.* . Fig. 51.F

KUN

vessels are arranged among bundles of fine tubes or fibres, '

as in muscles and nerves. In such parts, the meshes
usually have the form of a parallelogram, the short sides of
which may be from three to eight or ten times less than the
long ones; the long sides always corresponding to the axis
of the fibre or tube, by which it is placed. The appearance
of both the rounded and elongated meshes is much varied
according as the vessels composing them have a straight
or tortuous form. Sometimes the capillaries have a looped

* Fig. 50. Network of capillary vessels of the air-cells of the horse’s
lung, magnified. @, a, capillaries proceeding from 0, 6, terminal
branches of the pulmonary artery (after Frey).

+ Fig. 51. Injected capillary vessels of muscle, seen with a low

magnifying power (Sharpey).

THE CAPILLARIES. 159

arrangement, a single capillary projecting from the com-
_ mon network into some prominent organ, and returning
after forming one or more loops, as in the papille of the
tongue and skin. Whatever be the form of the capillary
network in any tissue or organ, it is, as a rule, found to
prevail in the corresponding parts of all animals.

The number of the capillaries and the size of the meshes
in different parts determine in general the degree of
vascularity of those parts. The parts in which the net-
work of capillaries is closest, that is, in which the meshes
or interspaces are the smallest, are the lungs and the
choroid membrane of the eye. In the iris and ciliary body
the interspaces are somewhat wider, yet very small. In the
human liver, the interspaces are of the same size, or even
smaller than the capillary vessels themselves. In the human
lung they are smaller than the vessels; in the human
kidney, and in the kidney of the dog, the diameter of the
injected capillaries, compared with that of the interspaces,
is in the proportion of one to four, or of one to three.
The brain receives a very large quantity of blood; but
the capillaries, in which the blood is distributed through
its substance are very minute, and less numerous than in
some other parts. Their diameter, according to E. H.
Weber, compared with the long diameter of the meshes,
being in the proportion of one to eight or ten; compared
with the transverse diameter, in the proportion of one to.
four or six. In the mucous membranes—for example, in
the conjunctiva—and in the cutis vera, the capillary vessels.
are much larger than in the brain, and the interspaces
narrower—namely, not more than three or four times
wider than'the vessels. In the periosteum the meshes are
much larger. In the cellular coat of arteries, the width
of the meshes is.ten times that of the vessels (Henle).

It may be held as a general rule, that the more active
the functions of an organ are, the more vascular it is; that
is, the closer is its capillary network and the larger its

160 "THE CIRCULATION.

supply of blood. Hence, the narrowness of the interspaces
in all glandular organs, in mucous membranes, and in
growing parts; their much greater width in bones, liga-
ments, and other very tough and comparatively inactive
tissues ; and the complete absence of vessels in cartilage,
the dense tendons of adults, and such” parts as those in
which, probably, very little organic change occurs after
they are once formed. But the general rule must be
modified by the consideration, that some organs, such as
the brain, though they have small and not very closely
arranged capillaries, may receive large supplies of blood
by reason of its more rapid movement. When an organ .
has large arterial trunks and a comparatively small supply
of capillaries, the movement of the blood through it will
be so quick, that it may, in a given time, receive as much
fresh blood as a more vascular part with smaller trunks,
though at any given instant the less vascular part will have —
in it a smaller quantity of blood.
In the Circulation in the Capillaries, as seen in any trans-
Fig. 52.* parent part of a living adult
animal by means of the mi-
croscope (fig. 52), the blood
flows with a constant equable
motion. In very young ani-
mals, the motion, though
continuous, is accelerated at
intervals corresponding to
the pulse in the larger ar-
teries, and a similar mo-
tion of the blood is also
seen in the capillaries of adtlt animals when they
are feeble: if their exhaustion is so great that the
power. of the heart is still more diminished, the red cor-
puscles are observed to have merely the periodic motion,

* Fig. 52. Capillaries in the web of the frog’s foot magnified.

en

oS fete es

es
;

THE CAPILLARIES. 161

and to remain stationary in the intervals; while, if the
debility of the animal is extreme, they even recede some-
what after each impulse, apparently because of the elasti-
city of the capillaries, and the tissues around them. These
observations may be added to those already advanced
(p. 132) to prove that, even in the state of great debility,
the action of the heart is sufficient to impel the blood
through the capillary vessels. Moreover, Dr. Marshall
Hall having placed the pectoral fin of ‘an eel in the field of
the microscope and compressed it by the weight of a heavy
probe, observed that the movement of the blood in the
capillaries became obviously pulsatory, the pulsations being
synchronous with the contractions of the ventricle. The
pulsatory motion of the blood in the capillaries cannot be
attributed to an action in these vessels; for, when the
animal is tranquil, they present not the slightest change in

their diameter. |
_ It is in the capillaries, that the chief resistance is offered
to the progress of the blood; for in them the friction of
the blood is greatly increased by the enormous multipli-
cation of the surface with which it is brought in contact.
The velocity of the blood is also in them reduced to its
minimum, because of the widening of the stream. If, as
Professor Miiller says, the sectional area of all the branches
of a vessel united were always the same as that of the
vessel from which they arise, and if the aggregate sec-
tional area of the capillary vessels were equal to that of
the aorta, the mean rapidity of the blood’s motion in the
capillaries would be the same as in the aorta and largest
y arteries; and if a similar correspondence of capacity existed
a in the veins and arteries, there would be an equal cor-
respondence in the rapidity of the circulation in them. It
is quite true, that the force with which the blood is pro-
pelled in the arteries, as shown by the quantity of blood
which escapes from them in a certain space of time, is
greater than that with which it moves in the veins;

M

162 THE CIRCULATION.

but this force has to overcome all the resistance offered im
the arterial and capillary system—the heart itself, indeed,
must overcome this resistance; so that the excess of the
force of the blood’s motion in the arteries is expended in
overcoming this resistance, and the rapidity of the circu-
lation in the arteries, even from the commencement of the
aorta, would be the same as in the veins and capillaries, if
the aggregate capacity of each of the three systems of
vessels were the same.

But since the aggregate sectional area of the branchew’ is
‘greater than that of the trunk from which they arise, the
rapidity of the blood’s motion will necessarily be greater
in the trunk, and will diminish in proportion as the
aggregate capacity of the vessels increases during their
ramification: in the same manner as, other things being
equal, the velocity of a stream diminishes as it widens.

The observations of Hales, E. H. Weber, and Valentin,.
agree very closely as to the rate of the blood in the capil-
laries of the frog: and the mean of their estimates gives
the velocity of the systemic capillary circulation at about
one inch per minute. Through the pulmonic capillaries,
the rate of motion, according to Hales, is about five times.
that through the systemic ones. The velocity in the
capillaries of warm-blooded animals is greater, but has
not yét been accurately estimated. If it be assumed to be
three times as great as in the frog, still the estimate may
seem too low, and inconsistent with the facts, which show
that the whole circulation is accomplished in about a
minute. But the whole length of capillary vessels, through
which any given portion of blood has to pass, probably
does not exceed =!,th of an inch; and therefore the time
required for each quantity of blood to traverse its own
appointed portion of the general capillary system will
scarcely amount to a second: while in the pulmonic capil-
lary system the length of time required will be much less
even than this.

THE CAPILLARIES. 163

The estimates given above are drawn from observations
of the movements of the red blood-corpuscles, which move
in the centre of the stream. At the circumference. of the
stream, in contact with the walls of the vessel, and adhering
to them, there is a layer of liquor sanguinis which appears
to be motionless. The existence of this still layer, as it is
termed, is inferred both from the general fact that such an
one exists in all fine tubes traversed by fluid, and from
what can be seen in watching the movements of the blood~
corpuscles. The red corpuscles occupy the middle of the
stream and move with comparative rapidity; the colourless
lymph-corpuscles run much more slowly by the walls of
the vessel; while next to the wall there is often a trans-
parent space in which the fluid appears to be at rest; for
if any of the corpuscles happen to be forced within it, they
move more slowly than before, rolling lazily along the side
of the vessel, and often adhering to its wall. Part of this
slow movement of the pale corpuscles and their occasional
stoppage may be due, as E. H. Weber has suggested, to
their having a natural tendency to adhere to the walls of
the vessels. .Sometimes, indeed, when the motion of the
blood is not strong, many of the white corpuscles collect
in a capillary vessel, and for a time entirely prevent the
passage of the red corpuscles. But there is no doubt that
such a still layer of liquor sanguinis exists next the walls
of the vessels, and it is between this and the tissues around
the vessels that those interchanges of particles take place
which ensue in nutrition, secretion, and absorption by the
blood-vessels; interchanges which are probably facilitated
by the tranquillity of the fluids between which they are
effected.

Until within the last few years it has been generally
supposed that the occurrence of any transudation from the
interior of the capillaries into the midst of the surrounding
tissues was confined, in the absence of injury, strictly to the
fluid part of the blood; in other words, that the corpuscles

M 2

164 THE CIRCULATION.

could not escape from the circulating stream, unless the
wall of the containing blood-vessel were ruptured. It is
true that an English physiologist, Dr. Augustus Waller,
affirmed in 1846, that he had seen blood-corpuscles, both
red and white, pass bodily through the wall of the capillary
vessel in which they were contained; and that, as no opening
could be seen before their escape, so none could be observed
afterwards—so rapidly was the part healed. But these ob-
servations did not attract much notice until the phenomena
of escape of the blood-corpuscles from the capillaries and
minute veins, apart from mechanical injury, was redis-
covered by Professor Cohnheim in 1867.

Professor Cohnheim’s experiment demonstrating the pass-
age of the corpuscles through the wall of the blood-vessel,
is performed in the following manner. A frog is curarized,
that is to say, paralysis is produced by injecting under the
skin a minute quantity of the poison called curare; and
the abdomen having been opened, a portion of small in-
testine is drawn out, and its transparent mesentery spread
out under a microscope. After a variable time, occupied
by dilatation, following contraction, of the minute vessels,
and accompanying quickening of the blood-stream, there
énsues a retardation of the current; and blood-corpuscles,
both red and white, begin to make their way through the
capillaries and small veins. ‘The process of extrusion of
the white corpuscles is thus described by Dr. Burdon San-
derson, and the passage of the red corpuscles occurs after
much the same fashion.

‘Simultaneously with the retardation, the leucocytes,
instead of loitering here and there at the edge of the axial
current, begin to crowd in numbers against the vascular wall,
as was long ago described by Dr. Williams. In this way
the vein becomes lined with a continuous pavement of these
bodies, which remain almost motionless, notwithstanding
that the axial current sweeps by them as continuously as
before, though with abated velocity. Now is the moment

THE CAPILLARIES. 165
at which the eye must be fixed on the outer contour of the
vessel, from which (to quote Professor Cohnheim’s words)
here and there minute, colourless, button-shaped elevations
spring, just as if they were produced by budding out of the
wall of the vessel itself. The buds increase gradually and
slowly in size, until each assumes the form of a hemispherical
projection, of width corresponding to that of a leucocyte.
Eventually the hemisphere is converted into a pear-shaped
body, the small end of which is still attached to the surface
of the vein, while the round part projects freely. Gradu-
ally the little mass of protoplasm removes itself further and
further away, and, as it does so, begins to shoot out delicate
prongs of transparent protoplasm from its surface, in no-
wise differing in their aspect from the slender thread by
which it is still moored to the vessel. Finally the thread
is severed, and the process is complete. The observer has
before him an emigrant leucocyte, which in all appreciable
-respects resembles those which have been already described
in the aqueous humour of the inflamed eye.”’

Various explanations of these remarkable phenomena
have been suggested. Probably the nearest to the truth
are those which attribute the chief share in the process to
the vital endowments with respect to mobility and contrac-
tility of the parts concerned—both of the corpuscles
(Bastian) and the capillary wall (Stricker). Dr. Sanderson
remarks, ‘‘ the capillary is not a dead conduit, but a tube of
living protoplasm. There is no difficulty in understanding
how the membrane may open to allow the escape of leuco-
cytes, and close again after they have passed out; for it is
one of the most striking peculiarities of contractile substance
that when two parts of the same mass are separated, and
again brought into contact, they melt together as if they
had not been severed.”

Hitherto, the escape of the corpuscles from the interior
of the blood-vessels into the surrounding tissues has been
studied chiefly in connection with pathology. But it is im-

166 THE CIRCULATION.

possible to say, at present, to what degree the discovery
may not influence all present notions regarding the nutri-
tion of the tissues, even in health. |

The circulation through the capillaries must, of necessity,
be largely influenced by that which occurs in the vessels on
either side of them—in the arteries or the veins; their in-
termediate position causing them to feel at once, so to speak,
any alteration in the size or rate of the arterial or venous
blood-stream. Thus, the apparent contraction of the
capillaries, on the application of certain irritating sub-
stances, and during fear, and their dilatation in blushing,
may be referred to the action of the small arteries, rather
than to that of the capillaries themselves. But largely as
the capillaries are influenced by these, and by the con-
ditions of the parts which surround and support them,
their own endowments must not be disregarded. They
must be looked upon, not as mere passive canals for
the passage of blood, but as possessing endowments of
their own, in relation to the circulation. The capillary
wall is, according to Stricker, actively living and con-
tractile; and there is no reason to doubt that, as such, it
must have an important influence in connection with that
nutritive exchange which goes on without cessation be-
tween the blood within and the tissues outside the capillary
vessel; a process which, under the name of vital capillary
force, has long been recognised as one of the means con-
cerned in the circulation of the blood.

The results of morbid action, as well as the phenomena of
health, strongly support the notion of the existence of
this so-called vital capillary attraction between the
blood and the tissues. For example, when the access
of oxygen to the lungs is prevented, the circulation
through the pulmonic capillaries is gradually retarded, the
blood-corpuscles cluster together, and their movement is
eventually almost arrested, even while the action of the
heart continues. In inflammation, also, the capillaries of

THE VEINS. 167

an inflamed part are enlarged and distended with blood,
which either moves very slowly or is completely at rest. In
both these cases the phenomena are local, and independent
of the action of the heart, and appear to result from some
alteration in the blood, which increases the adhesion of its
particles to one another, and to the walls of the capillaries,
to an amount which the propelling action of the heart is
not able to overcome. |

It may be concluded then, that the capillaries, which are
formed of a simple cellular membrane, can of themselves
exercise no such direct influence on the movement of their
contents as to be at all comparable in degree to that which
is exercised by the arteries or veins: yet that the constant
interchange of relations between the blood within and the
tissues outside these vessels does in some measure facilitate
the movement of blood through the capillary system, and
constitute one of the assistant forces of the circulation.

THE VEINS.

In structure the coats of veins bear a general resemblance
to those of arteries. Thus, they possess an outer, middle,
and internal coat. The outer coat is constructed of areolar
tissue like that of the arteries, but is thicker. In some
‘veins it contains muscular fibre-cells.

The middle coat is considerably thinner than that of the
arteries; and, although it contains circular unstriped mus-
cular fibres or fibre-cells, these are mingled with a larger
proportion of yellow elastic and white fibrous tissue. In
the large veins near the heart, namely, the vene cave and
pulmonary veins, the middle coat is replaced, for some
distance from the heart, by circularly arranged striped
muscular fibres, continuous with those of the auricles.

The internal coat of veins is less brittle than the corre-
sponding coat of an artery, but in other respects resembles
at closely.

The chief influence which the veins have in the circula-

-

168 THE CIRCULATION.

tion, is effected with’ the help of the valves, which are placed
in all veins’ subject to local pressure from the muscles.
between or near which they run. The general construction
of these valves is similar to that of the semilunar valves of
the aorta and pulmonary artery, already described (p. 108) ;
but their free margins are turned in the opposite direction,
i.e. towards the heart, so as to stop any movement of blood
backward in the veins. They are commonly placed in pairs,
at various distances in different veins, but almost uniformly
in each (fig. 53). In the smaller veins, single valves are-
often met with; and three or four are sometimes placed
together, or near one another, in the largest veins, such as.
the subclavian, and at their junction with the jugular veins.
Fig. 53.* The valves are semi-
lunar; the unattached
edge being in some
examples concave, in
others straight. They
are composed of inex-
tensile fibrous tissue,
and are covered with
epithelium like that
lining the veins.
During the ‘period of
their inaction, when
the venous blood is flowing in its proper direction, they
lie by the sides of the veins; but when in action, they close.
together like the valves of the arteries, and offer a com-
plete barrier to any backward movement of the blood
(figs. 54 and 55).
Valves are not equally numerous in all veins, and im

* Fig. 53. Diagrams showing valves of veins. A, Part of a vein laid
open and spread out, with two pairs of valves. B. Longitudinal section
of a vein, showing the apposition of the edges of the valves in their
closed state. C. Portion of a distended vein, exhibiting a swelling in
the situation of a pair of valves.

VALVES OF VEINS. 169

many they are absent altogether. They are most numerous
in the veins of the extremities, and more so in those of the
leg than the arm. They are commonly absent in veins of
less than a line in diameter, and, as a general rule, there
are few or none in those which are not subject to muscular
- pressure. Among those veins which have no valves may be
mentioned the superior and inferior vena cava, the trunk
and branches of the portal vein, the hepatic and renal
veins, and the pulmonary veins; those in the interior
of the cranium and vertebral column, those of the bones,
and the trunk and branches of the umbilical vein are also
destitute of valves.

The principal obstacle to the circulation is already over-
come when the blood has traversed the capillaries ; and the
force of the heart which is not yet consumed, is sufficient
to complete its passage through the veins, in which the
obstructions to its movement are very slight. For the for-
midable obstacle supposed to be presented by the gravita-
tion of the blood, has no real existence, since the pressure
exercised by the column of blood in the arteries, will be
always sufficient to support a column of venous blood of the
same height as itself: the two columns mutually balancing
each other. Indeed, so long as both arteries and veins con-
tain continuous columns of blood, the force of gravitation,
whatever be the position of the body, can have no power to
move or resist the motion of any part of the blood in any
direction. The lowest blood-vessels have, of course, to bear:
the greatest amount of pressure ; the pressure on each part
being directly proportionate to the height of the column of
blood above it: hence their liability to distension. But
this pressure bears equally on both arteries and veins, and
cannot either move, or resist the motion of, the fluid they
contain, so long as the columns of fluid are of equal height
in both, and continuous. Their condition may, in this respect
be compared with that of a double bent tube, full of fluid,
held vertically ; whatever be the height and gravitation of

{70 THE CIRCULATION.

the columns of fluid, neither of them can move of its own
weight, each being supported by the other; yet the least
pressure on the top of either column will lift up the other :
so, when the body is erect, the least pressure on the column
of arterial blood may lift up the venous blood, and, were
it not for the valves, the least pressure on the venous might
lift up the arterial column.

In experiments to determine what proportion of the force
of the left ventricle remains to propel the blood in the veins,
Valentin found that the pressure of the blood in the jugular
vein of a dog, as estimated by the hemadynamometer, did

-not amount to more than 54 or =); of that in the carotid
artery of the same animal; and this estimate is confirmed,
in the instances of several other arteries and their corre-
sponding veins, by Mogk. In the upper part of the inferior
vena cava, Valentin could scarcely detect the existence of
any pressure, nearly the whole force received from the heart
having been, apparently, consumed during the passage of
the blood through the capillaries. But slight as this re-
maining force might be (and the experiment in which it
was estimated would reduce the force of the heart below
its natural standard), it would be enough to complete
the circulation of the blood; for, as already stated, the
spontaneous dilatation of the auricles and ventricles, though
it may not be forcible enough to assist the movement of
blood into them, is adapted to offer to that movement no
obstacle.

Very effectual assistance to the flow of blood in the veins
is afforded by the action of the muscles capable of pressing
on such veins as have valves.

The effect of muscular pressure on such veins may be thus
explained. When pressure is applied to any part of a vein,
and the current of blood in it is obstructed, the portion
behind the seat of pressure becomes swollen and distended
as far back as to the next pair of valves. These, acting like
the arterial valves, and being, like them, inextensile both in

PRESSURE IN VEINS. 171

themselves and at their margins of attachment, do not
follow the vein in its distension, but are drawn out towards
the axis of the canal. Then, if the pressure continues on
the vein, the compressed blood, tending to move equally in
all directions, presses the valves down into contact at their
free edges, and they close the vein’ and prevent regurgita-
tion of the blood. Thus, whatever force is exercised by
the pressure of the muscles on the veins, is distributed partly
in pressing the blood onwards in the proper course of the
circulation, and partly in pressing it backwards and closing
the valves behind.

The circulation might lose as much as it gains by such
compression of the veins, if it were not for the numerous
anastomoses by which they communicate, one with another ;

Fig. 54* Fig. 55-7

for through these, the closing up of the venous channel by
the backward pressure is prevented from being any serious

* Fig. 54. Vein with valves open (Dalton).
{ Fig. 55. Vein with valves closed ; stream of blood passing off by
lateral channel (Dalton).

172 THE CIRCULATION.

hindrance to the circulation, since the blood, of which the
onward course is arrested by the closed valves, can at once
pass through some anastomosing channel, and proceed on its
_ way by another vein (figs. 54 and 55). Thus, therefore, the
effect of muscular pressure upon veins which have valves, is
turned almost entirely to the advantage of the circulation ;
the pressure of the blood onwards is all advantageous, and
the pressure of the blood backwards is prevented from being
a hindrance by the closure of the valves and the anastomoses
of the veins.

The effects of such muscular pressure are well shown by
the acceleration of the stream of blood when, in venesec-
tion, the muscles of the fore-arm are put in action, and by
the general acceleration of the circulation during active
exercise; and the numerous movements which are con-
tinually taking place in the body while awake, though
their single effects may be less striking, must be an im-
portant auxiliary to the venous circulation. Yet they
are not essential; for the venous circulation continues
‘unimpaired in parts at rest, in paralysed limbs, and in
parts in which the veins are not subject to any muscular
pressure. |

Besides the assistance thus afforded by muscular pressure
to the movement of blood along veins possessed of valves,
it has been discovered by Mr. Wharton Jones that, in the
web of the bat’s wing, the veins are furnished with valves,
and possess the remarkable property of rhythmical contrac-
tion and a dilatation, whereby the current of blood within
them is distinctly accelerated. The contraction occurred,
on an average, about ten times in a minute; the existence
of valves preventing regurgitation, the entire effect of the
contractions was auxiliary to the onward current of blood.
Analogous phenomena have been now frequently observed
in other animals.

EFFECTS OF RESPIRATION. 173

Agents Concerned in the Circulation of the Blood.

The agents concerned in the circulation of the blood
which have been now described, may be thus enume-
rated :—

1. The action of the heart and of the arteries.

2. The vital capillary force exercised in the capil-
laries.

3. The possible slight action of the muscular coat of
veins; and, much more, the contraction of muscles capable
of acting on veins provided with valves.

It remains only to consider (4) the influence of the
respiratory movements on the circulation.

Although the continuance of the respiratory movements
is essential to the circulation of the blood, and although
their cessation is followed, within a very few minutes, by
that of the heart’s action also, yet their direct mechanical |
influence on the movement of the current of blood is pro-
bably, under ordinary circumstances, but slight. The effect
of expiration in increasing the pressure of the blood in the
arteries is minutely illustrated by the experiments of Lud-
wig. It acts as the pressure of contracting muscles does
upon the veins, and is advantageous to the onward move-
ment of arterial blood, inasmuch as all movement backwards:
into the heart, which would otherwise occur at the same
moment and from the same cause, is prevented by the force
of the onward stream of blood from the contracting ven-
tricle, and in the intervals of this contraction by the closure
of the semilunar valves. Under ordinary circumstances,
and with a free passage through the capillaries of the lungs,
the effect of expiration on the stream of blood in the veins
is also probably to assist, rather than retard its movement
in the proper direction. For, with no obstruction in front,
there is the force of the blood streaming into the heart from
behind, to prevent any tendency to a backward flow, even

174 THE CIRCULATION.

apart from what may be effected by the presence of the
valves of the venous system.

It is true that in violent expiratory efforts there is a.
certain retardation of the circulation in the veins. The
effect of such ‘retardation is shown in the swelling-up of
‘the veins of the head and neck, and the lividity of the face,
during coughing, straining, and similar violent expiratory
efforts ; the effects shown in these instances being due both
to some actual regurgitation of the blood in the great
veins, and to the accumulation of blood in all the veins, from
their being constantly more and more filled by the influx
from the arteries.

But strong expiratory efforts, as in straining and the
like, are not fairly comparable to ordinary expiration, inas-
much as they are instances of more or less interference
with expiration, and involve probably circumstances lead-
ing to obstruction of the circulation in the pulmonary
capillaries, such as are not present in the ordinary rhyth-
mical exit of air from the lungs.

The act of inspiration is favourable to the venous circu-
lation, and its effect is not counterbalanced by its tendency ~
to draw the arterial, as well as the venous, blood towards
the cavity of the chest. When the chest is enlarged in
inspiration, the additional space within it is filled chiefly
by the fresh quantity of air which passes through the
trachea and bronchial passages to the vesicular structure
of the lungs. But the blood being, like the air, subject to
the atmospheric pressure, some of it also.is at the same time
pressed towards the expanding cavity of the chest, and
therein towards the heart. The effect of this on the arterial
current is hindered by the aortic valves, while they are
closed, and by the forcible outward stream of blood from
the ventricles when they are open; while, on the other
hand, there is nothing to prevent an increased afflux of
blood to the auricles through the large veins.

Sir David Barry was the first who showed plainly this.

VELOCITY OF THE CIRCULATION. 175

effect of inspiration on the venous circulation; and he
mentions the following experiment in proof of it. He
introduced one end of a bent glass tube into the jugular
vein of an animal, the vein being tied above the point
where the tube was inserted; the inferior end of the tube
was immersed in some coloured fluid. He then observed
that at the time of each inspiration the fluid ascended in
the tube, while during expiration it either remained
stationary, or even sank. Poiseuille confirmed the truth
of this observation, in a more accurate manner, by means of
his hemadynamometer. And a like confirmation has beem
since furnished by Valentin, and in minute details by Ludwig.

The effect of inspiration on the veins is observable only
in the large ones near the thorax. Poiseuille could not
detect it by means of his instrument in veins more distant
from the heart,—for example, in the veins of the extremi-
ties. And its beneficial effect would be neutralized were
it not for the valves; for he found that, when he repeated
Sir D. Barry’s experiments, and passed the tube so far
along the veins that it went beyond the valves nearest to:
the heart, as much fluid was forced back into the tube in
every expiration as was drawn in through it in every
inspiration.

Dr. Burdon Sanderson’s experiments have proved more
directly that inspiration is favourable to the circulation,
inasmuch as, during it, the tension of the arterial system
is increased. And it is only when the respiratory orifice
is closed, as by plugging the trachea, that inspiratory
efforts are sufficient to produce an opposite effect—to
diminish the tension in the arteries.

On the whole, therefore, the respiratory movements of
the chest are advantageous to the circulation.

Velocity of Blood in the Veins.

The velocity of the blood is greater in the veins than in
the capillaries, but less than in the arteries; and with this

176 THE CIRCULATION.

fact may be remembered the relative capacities of the
arterial and venous systems; for since the veins return to
the heart all the blood that they receive from it in a given
time through the arteries, their larger size and propor-
tionally greater number must compensate for the slower
movement of the blood through them. If an accurate
estimate of the proportionate areas of arteries and the veins
corresponding to them could be made, we might, from the
velocity of the arterial current, calculate that of the venous.
An usual estimate is, that the capacity of the veins is about
twice or three times as great as that of the arteries, and
that the velocity of the blood’s motion is, therefore, about
twice or three times as great in the arteries as in the veins.
Some doubt has, however, been lately expressed regarding
the accuracy of this calculation, and the matter, therefore,
must be considered not yet settled. The rate at which the
blood moves in the veins gradually increases the nearer it
approaches the heart, for the sectional area of the venous
trunks, compared with that of the branches opening into
them, becomes gradually less as the trunks advance towards

the heart.
Velocity of the Circulation.

Having now considered the share which each of the cir-
culatory organs has in the propulsion and direction of the
blood, we may speak of their combined effects, especially
in regard to the velocity with which the movement of the
blood through the whole round of the circulation is accom-
plished. As Miiller says, the rate of the blood’s motion in
the vessels must not be judged of by the rapidity with
which it flows from a vessel when divided. In the latter
case, the rate of motion is the result of the entire pressure
to which the whole mass of blood is subjected in the vas-
cular system, and which at the point of the incision in the
vessel meets with no resistance. In the closed vessels, on
the contrary, no portion of blood can be moved forwards

VELOCITY OF THE CIRCULATION. 177

except by impelling on the whole mass, and by overcoming
the resistance arising from friction in the smaller vessels.

From the rate at which the blood escapes from opened:
vessels we can only judge, in general, that its velocity is, as
already said, greater in arteries than in veins, and in both
these greater than in the capillaries. More satisfactory data
for the estimates are afforded by the results of experiments
to ascertain the rapidity with which poisons introduced
into the blood are transmitted from one part of the vascular
system to another. From eighteen such experiments on
horses, Hering deduced that the time required for the
passage of a solution of ferrocyanide of potassium, mixed
with the blood, from one jugular vein (through the right
side of the heart, the pulmonary circulation, the left cavities
of the heart, and the general circulation) to the jugular
vein of the opposite side, varies from twenty to thirty
seconds. The same substance was transmitted from the
jugular vein to the great saphena in twenty seconds; from
the jugular vein to the masseteric artery, in between fifteen
and thirty seconds ; to the facial artery, in one experiment,
in between ten and fifteen seconds; in another experiment
in between twenty and twenty-five seconds; in its transit
from the jugular vein to the metatarsal artery, it occupied
between twenty and thirty seconds, and in one instance
more than forty seconds. The result was nearly the same
whatever was the rate of the heart’s action.

Poiseuille’s observations accord completely with the
_ above, and show, moreover, that when the ferrocyanide
is injected into the blood with other substances, such as
acetate of ammonia, or nitrate of potash (solutions of
which, as other experiments have shown, pass quickly
through capillary tubes), the passage from one jugular
vein to the other is effected in from eighteen to twenty-
four seconds; while, if instead of these, alcohol is added,
the passage is not completed until from forty to forty-five

seconds after injection. Still greater rapidity of transit
N

178. THE CIRCULATION.

has been observed by Mr. J. Blake, who found that
nitrate of baryta injected into the jugular vein of a horse
could be detected in blood drawn from the carotid artery
of the opposite side in from fifteen to twenty seconds after
the injection. In sixteen seconds a solution of nitrate of
potash, injected into the jugular vein of a horse, caused
complete arrest of the heart’s action, by entering and
diffusing itself through the coronary arteries. In a dog,
the poisonous effects of strychnia on the nervous system
were manifested in twelve seconds after injection into the
jugular vein; in a fowl, in six and a half seconds, and in
a rabbit in four and a half seconds.

In all these experiments, it is assumed that the sub-
stance injected moves with the blood, and at the same rate
as it, and does not move from one part of the organs of
circulation to another by diffusing itself through the blood
or tissues more quickly than the blood moves. The
assumption is sufficiently probable, to be considered nearly
certain, that the times above mentioned, as occupied in
the passage of the injected substances, are those in which
the portion of blood, into which each was injected, was
carried from one part to another of the vascular system.
It would, therefore, appear that a portion of blood can
traverse the entire course of the circulation, in the horse,
in half a minute; of course it would require longer to
traverse the vessels of the most distant part of the ex-
tremities than to go through those of the neck; but taking
an average length of vessels to be traversed, and assuming,
as we may, that the’movement of blood in the human
subject is not slower than in the horse, it may be concluded
that one minute, which is the estimate usually adopted
of the average time in which the blood completes its entire
circuit in man, is rather above than below the actual rate.

Another mode of estimating the general velocity of the
circulating blood, is by calculating it from the quantity of
blood supposed to be contained in the body, and from the

VELOCITY OF THE CIRCULATION. 179

quantity which can pass through the heart in each of its
actions. But the conclusions arrived at by this method
are less satisfactory. For the estimates both of the total
quantity of blood, and of the capacity of the cavities of
the heart, have as yet only approximated to the truth.
Still, the most careful of the estimates thus made accord
with those already mentioned; for Valentin has, from
these data, calculated that the blood may all pass through
the heart in from 43% to 622 seconds.

The estimate for the speed at which the blood may be
seen moving in transparent parts, is not opposed to this.
For, as already stated (p. 162), though the movement
through the capillaries may be very slow, yet the length
of capillary vessel through which any portion of blood has
to pass is very small. Even if we estimate that length at
the tenth of an inch, and suppose the velocity of the blood
' therein to be only one inch per minute, then each portion
of blood may traverse its. own distance of the capillary
system in about six seconds. There would thus be plenty
-of time left for the blood to travel through its circuit in
the larger vessels, in which the greatest length of tube
that it can have to traverse in the human subject does not
exceed ten feet.

All the estimates here given are averages; but of course
the time in which a given portion of blood passes from
one side of the heart to the other, varies much according
to the organ it has to traverse. The blood which circulates
from the left ventricle, through the coronary vessels, to the
right side of the heart, requires a far shorter time for the
completion of its course than the blood which flows from
the left side of the heart to the feet, and back again to the —
right side of the heart; for the circulation from the left to
the right cavities of the heart may be represented as form-
ing a number of arches, varying in size, and requiring
proportionately various times for the blood to traverse
them; the smallest of these arches being formed by the

N 2

180 THE CIRCULATION.

circulation through the coronary vessels of the heart itself.
The course of the blood from the right side of the heart,
through the lungs to the left, is shorter than most of the
arches described by the systemic circulation, and in it the
blood flows, eeteris paribus, much quicker than in most of
the vessels which belong to the aortic circulation. For
although the quantity of blood contained, at any instant,.
in the greater circulation of the body, is far greater than
the quantity within the lesser circulation; yet, in any giver
space of time, as much blood must pass through the lungs.
as passes in the same time through the systemic circulation.
If the systemic vessels contain five times as much blood as.
the pulmonary, the blood in them must move five times as.
slow as in these; else, the right side of the heart would
be either overfilled or not filled enough.

Peculiarities of the Circulation in different Parts.

The most remarkable peculiarities attending the circula-
tion of blood through different organs are observed in the
cases of the lungs, the liver, the brain, and the erectile organs.
The pulmonary and portal circulations have been already
alluded to (pp. IOI, 102), and will be again noticed when
considering the functions of the lungs and liver.

The chief circumstances requiring notice, in relation to
the cerebral circulation, are observed in the arrangement and
distribution of the vessels of the brain, and in the con-
ditions attending the amount of blood usually contained
within the cranium.

The functions of the brain seem to require that it should
receive a large supply of blood. This is accomplished
through the number and size of its arteries, the two internal
carotids, and the two vertebrals. But it appears to be
further necessary that the force with which this blood is
sent to the brain should be less, or at least, subject to less
variation from external circumstances, than it is in other
parts. This object is effected by several provisions; such

\

CEREBRAL CIRCULATION, 18I

as the tortuosity of the large arteries, and their wide anas-
tomoses in the formation of the circle of Willis, which will
ansure that the supply of blood to the brain may be uni-
form, though it may by an accident be diminished, or
in some way changed, through one or more of the principal
arteries. The transit of the large arteries through bone,
especially the carotid canal of the temporal bone, may
prevent any undue distension; and uniformity of supply
is further insured by the arrangement of the vessels in
the pia mater, in which, previous to their distribution to
the substance of the brain, the large arteries break up and
divide into innumerable minute branches ending in capil-
laries, which, after frequent communications with one
another, enter the brain, and carry into nearly every part
of it uniform and equable streams of blood.

The arrangement of the veins within the cranium is also
peculiar. The large venous trunks or sinuses are formed
so as to be scarcely capable of change of size; and com-
posed, as they are, of the tough tissue of the dura mater,
and, in some instances, bounded on one side by the bony
cranium, they are not compressible by any force which the
fulness of the arteries might exercise through the substance
of the brain; nor do they admit of distension when the
flow of venous blood from the brain is obstructed.

The general uniformity in the supply of blood to the
brain, which is thus secured, is well adapted, not only to
its functions, but also to its condition as a mass of nearly
incompressible substance placed in a cavity with unyielding
walis. These conditions of the brain and skull have ap-
peared, indeed, to some, enough to justify the opinion
that the quantity of blood in the brain must be at all times
the same; and that the quantity of blood received within
any given time through the arteries must be always, and
at the same time, exactly equal to that removed by the
veins. In accordance with this supposition, the symptoms
commonly referred to either excess or deficiency of blood

182 THE CIRCULATION.

in the brain, were ascribed to a disturbance in the balance
between the quantity of arterial and that of venous blood.
Some experiments ‘performed by Dr. Kellie appeared to
establish the correctness of this view. But Dr. Burrows.
having repeated these experiments, and performed addi-
tional ones, obtained different results. He found that in
animals bled to death, without any aperture being made
in the cranium, the brain became pale and anzemic like
other parts. And in proof that, during life, the cerebral
circulation is influenced by the same general circumstances.
that influence the circulation elsewhere, he found conges-
tion of the cerebral vessels in rabbits killed by strangling
or drowning; while in others, killed by prussic acid, he
observed that the quantity of blood in the cavity of the
cranium was determined by the position in which the
animal was placed after death, the cerebral vessels being
congested when the animal was suspended with its head
downwards, and comparatively empty when the animal —
was kept suspended by the ears. He concluded, therefore,
that although the total volume of the contents of the
cranium is probably nearly always the same, yet the
quantity of blood in it is liable to variation, its increase or
diminution being accompanied by a simultaneous diminu-
tion or increase in the quantity of the cerebro-spinal fluid,
which, by readily admitting of being removed from one
part of the brain and spinal cord to another, and of being
rapidly absorbed, and as readily effused, would serve as a
kind of supplemental fluid to the other contents of the
cranium, to keep it uniformly filled in case of variations in.
their quantity. And there can be no doubt that, although
the arrangements of the blood-vessels, to which reference
has been made, ensure to the brain an amount of blood
which is tolerably uniform, yet, inasmuch as with every
beat of the heart and every act of respiration, and under
many other circumstances, the quantity of blood in the
cavity of the cranium is constantly varying, it is plain that,

CIRCULATION IN ERECTILE STRUCTURES. 183

were there not provision made for the possible displace-
ment of some of the contents of the unyielding bony
case in which the brain is contained, there would be often
alternations of excessive pressure with insufficient supply
of blood. Hence we may consider that the cerebro-spinal
fluid in the interior of the skull not only subserves the
mechanical functions of fat in other parts as a packing
material, but by the readiness with which it can be dis-
placed into the spinal canal, provides the means whereby
undue pressure and insufficient supply of blood are equally
prevented.

Circulation in erectile structures.—The instances of greatest
variation in the quantity of blood contained, at different
times, in the same organs, are found in certain structures
which, under ordinary circumstances, are soft and flaccid,
but, at certain times, receive an unusually large quantity
of blood, become distended and swollen by it, and pass into
the state which has been termed erection. Such structures
are the corpora cavernosa and corpus spongiosum of the
penis in the male, and the clitoris in the female; and, to
a less degree, the nipple of the mammary gland in both
sexes. The corpus cavernosum penis, which is the best
example of an erectile structure, has an external fibrous
membrane or sheath; and from the inner surface of the
latter are prolonged numerous fine lamelle which divide
its cavity into small compartments looking like cells when
they are inflated. Within these is situated the plexus of
veins upon which the peculiar erectile property of the
organ mainly depends. It consists of short veins which
very closely interlace and anastomose with each other in
all directions, and admit of great variation of size, col-
lapsing in the passive state of the organ, but, for erection,
capable of an amount of dilatation which exceeds beyond
comparison that of the arteries and veins which convey the
blood to and from them. ‘The strong fibrous tissue lying
in the intervals of the venous plexuses, and the external

184 | THE CIRCULATION.

fibrous membrane or sheath with which it is connected,
limit the distension of the vessels, and, during the state of
erection, give to the penis its condition of tension and
firmness. The same general condition of vessels exists in
the corpus spongiosum urethra, but around the urethra
the fibrous tissue is much weaker than around the body of
the penis, and around the glands there is none. The
venous blood is returned from the plexuses by compara-
tively small veins; those from the glans and the fore part
of the urethra empty themselves into the dorsal vein of the
penis ; those from the corpus cavernosum pass into deeper
veins which issue from the corpora cavernosa at the crura
penis; and those from the rest of the urethra and bulb

pass more directly into the plexus of the veins about the —

prostate. For all these veins one condition is the same ;
namely, that they are liable to the pressure of muscles
when they leave the penis. The muscles chiefly con-
cerned in this action are the erector penis and accelerator
urine.

Erection results from the distension of the venous plex-
uses with blood. The principal exciting cause in the erec-
tion of the penis is nervous irritation, originating in the
part itself, or derived from the brain and spinal cord. The
nervous influence is communicated to the penis by the pudic
nerves, which ramify in its vascular tissue: and Guenther
has observed, that, after their division in the horse, the
penis is no longer capable of erection. It affords a good
example of the subjection of the circulation in an indivi-
dual organ to the influence of the nerves; but the mode
in which they excite a greater influx of blood is not with
certainty known.

The most probable explanation is that offered by Pro-
fessor Kolliker, who’ ascribes the distension of the venous
plexuses to the influence of organic muscular fibres, which
are found in abundance in the corpora cavernosa of the
penis, from the bulb to the glans, also in the clitoris and

CIRCULATION IN ERECTILE STRUCTURES. 185

other parts capable of erection. While erectile organs
are flaccid and at rest, these contractile fibres exercise an
amount of pressure on the plexuses of vessels distributed
amongst them, sufficient to prevent their distension with
blood. But when through the influence of their nerves,
these parts are stimulated to erection, the action of these
fibres is suspended, and the plexuses thus liberated from
pressure, yield to the distending force of the blood, which,
probably, at the same time arrives in greater quantity,

\ owing to a simultaneous dilatation of the arteries of the

parts, and thus the plexuses become filled, and remain so
until the stimulus to erection subsides, when the organic
muscular fibres again contract, and so gradually expel the
excess of blood from the previously distended vessels.
The influence of cold in producing extreme contraction and
shrinking of erectile organs, and the opposite effect of
warmth in inducing fulness and distension of these parts,
are among the arguments used by Kolliker in support of
this opinion.

The accurate dissections and experiments of Kobelt,
extending and confirming those of Le Gros Clark and
Krause, have shown, that this influx of the blood, however
explained, is the first condition necessary for erection, and —
that through it alone much enlargement and turgescence
of the penis may ensue. But the erection is probably
not complete, nor maintained for any time except when,
together with this influx, the muscles already mentioned
contract, and by compressing the veins, stop the efflux of
blood, or prevent it from being as great as the influx.

It appears to be only the most perfect kind of erection
that needs the help of muscles to compress the veins; and
none such can materially assist the erection of the nipples,
or that amount of turgescence, just falling short of erec-
tion, of which the spleen and many other parts are capable.
For such turgescence nothing more seems necessary than
a large plexiform arrangement of the veins, and such

186 RESPIRATION.

arteries as may admit, upon local occasions, augmented
quantities of blood.

The Influence of the Nervous System on the circulation
in the blood-vessels will be considered in Chap. XVII.

CHAPTER VII.
RESPIRATION.

As the blood circulates through the various parts of the
body, and fulfils its office by nourishing the several
tissues, by supplying to secreting organs the materials
necessary for their secretions, and by the performance of
other duties with which it is charged, it is deprived,of
part of its nutritive constituents, and receives impurities
which need removal from the body. It is, therefore,
necessary that fresh supplies of nutriment shouldbe con-
tinually added to the blood, and that provision should

be made for the removal of the impurities. The first of —

these objects is accomplished by the processes of digestion
and absorption. The second is principally effected by the
agency of the various excretory organs, through which are
removed the several impurities with which the blood is

charged, whether these impurities are derived altogether ©

from the degenerations of tissue, or in part also from the
elements of unassimilated food. One of the most important
and abundant of the impurities is carbonic acid, the re-
moval of which and the introduction of fresh quantities of
oxygen, constitute the chief purpose of respiration—a

Py et mets 2.

STRUCTURE OF THE LUNGS. 187

process which, because of its intimate relation to the cir-
culation, may be considered here, rather than with the
other excretory functions.

Position and Structure of the Lungs.

The lungs occupy the greater portion of the chest, or
uppermost of the two cavities into which the body is
divided by the diaphragm (fig. 31). They are of a spongy
elastic texture, and on section appear to the naked eye as
if they were in great part solid organs, except here and
there, at certain points, where branches of the bronchi or
air-tubes may have been cut across, and show, on their
surface of the section, their tubular structure.

In fact, however, the lungs are hollow organs, and we
may consider them as really two bags containing air, each
of which communicates by a separate orifice with a common
air-tube (fig. 31), through the upper portion of which,
the larynz, they freely communicate with the external

Fig. 56*.

atmosphere. The orifice of the larynx is guarded by
muscles, and can be opened or closed at will.

—— SS eee - ees

* Fig. 56. Transverse section of the chest (after Gray).

188 RESPIRATION,

It has been said, in the preceding chapter that each
Jung is enveloped in a distinct fibrous bag, with a smooth,
slippery lining, and that the outer smooth surface of the
lung glides easily on the inner smooth -surface of the
bag which envelops it. This enveloping bag, which is
called the pleura, is easily seen in the dead subject; and
when it is opened, as in an ordinary post-mortem examina-
tion, there is a considerable space left, by the elastic recoil
of the lung, between the outer surface of the lung and the
inner surface of the pleura, which is left sticking, so to
speak, to the inner surface of the walls and floor of the
chest.

This space, however, between the lung and the pleura
does not exist (except in some cases of disease) so long as
the chest is not opened ; and, while considering the subject
of normal healthy respiration, we may discard altogether
the notion of any space or cavity between the lung and
the wall of the chest. So far as the movement of the lung
is concerned it might be adherent completely to the chest-
wall, inasmuch as they accompany each other in all their
movements; only there is a slight gliding of the smooth
surface of the lung on the smooth inner surface of the
pleura, but no separation, in the slightest degree, of one
from the other.*

The trachea, or tube through which air passes to the
lungs, divides into two branches—one for each lung ;
and these primary branches, or bronchi, after entering the

* It may be mentioned, that the smooth covering of the lung is
really continuous with the inner smooth lining of the walls and floor of
the chest, as will be readily seen in fig. 56. Hence the membrane
which covers the lung is called the visceral layer of the pleura, and that
which lines the walls and floor of the chest the parietal layer. _The
appearance of a cavity or space (fig. 56) between the visceral layer of
pleura (covering the lungs) and the parietal layer (covering the inner
surface of the wall of the chest and upper part of the diaphragm) is
only inserted for the sake of distinctness.

——

———— = —

7

STRUCTURE OF THE LUNGS. 189

substance of the organ, divide and subdivide into a number
of smaller and smaller branches, which penetrate to every
part of the organ, until at length they end in the smaller
subdivisions of the lung called lobules. All the larger
branches have walls formed of tough membrane, contain-
ing portions of cartilaginous rings, by which they are held
open, and unstriped muscular fibres, as well as longi-
tudinal bundles of elastic tissue. They are lined by
mucous membrane, the surface of which, like that of the

larynx and trachea, is covered with vibratile ciliary epi-
thelium (fig. 58).
As the bronchi divide they become smaller and smaller,

* Fig. 57. <A diagrammatic representation of the heart and great
vessels in connection with the lungs—%. The pericardium has been
removed, and the lungs are turned aside. 1, right auricle ; 2, vena cava
superior ; 3, vena cava inferior ; 4, right ventricle ; 5, stem of the pul-
monary artery; @ a, its right and left branches; 6, left auricular

appendage ; 7, left ventricle ; 8, aorta; 9, 10, the two lobes of the left

lung ; II, 12, 13, the three lobes of the right lung; 0 6, right and left
bronchi; v v, right and left wpper pulmonary veins.

190 RESPIRATION.

and their walls thinner; the cartilaginous rings, especially

becoming scarcer and more irregular, until, in the smaller
bronchial tubes, they are represented only by minute and
scattered cartilaginous flakes. And when the bronchi, by
successive branches, are reduced to about 31, of an inch
in diameter, they lose their cartilaginous element alto-
gether, and their walls are formed only of a tough, fibrous,
elastic membrane, with traces of circular muscular fibres;
they are still lined, however, by a thin mucous membrane,
with ciliated epithelium.

Each lung is partially subdivided into separate portions,
called lobes ; the right lung into three lobes, and the left
lung into two o (fig. 5 7). Each of ace. lide lobes, again, is

composed of a large number of minute parts, called lobules.
Each pulmonary lobule may be considered a lung in
miniature, consisting, as it does, of a branch of the bron-
chial ‘tube, of air-cells, blood-vessels, nerves, and lymphatics,
with a sparing amount of areolar tissue.

On entering a lobule, the small bronchial tube divides

* Fig. 58. Ciliary epithelium of the human trachea magnified 350
diameters. a, Layer of longitudinally arranged elastic fibres ; 0, Base-
ment membrane; ¢, Deepest cells, circular in form; d, Intermediate
elongated cells ; e, Outermost layer of cells fully developed and bearing
cilia (from Kolliker).

Se 2

STRUCTURE OF THE LUNGS. 1Qr

and subdivides; its walls, at the same time, becoming
thinner and thinad, until at length ‘they are formed only
of a thin membrane of areolar and elastic tissue, lined by
a layer of squamous epithelium, not provided with cilia. At
the same time, they are altered in shape; each of the
minute terminal branches widening out funnel-wise, and
its walls being pouched out irregularly into small saccular
dilatations, called air-cells (fig. 59). Such a funnel-shaped
terminal branch of the bronchial tube, with its group of
pouches or air-cells, has -been called an infundibulum
(fig. 59), and the irregular oblong space in its centre,
with which the air-cells communicate, an intercellular
passage.

The air-cells may be
placed singly, like recesses
from the intercellular pas-
sage, but more often they
are arranged in groups or
even in rows, like minute
sacculated tubes; so that
a short series of cells,
all communicating with
one another, open by a
common orifice into the
tube. The cells are of
various forms, according
to the mutual pressure to
which they are subject ;
their walls are nearly in contact, and they vary from
5, to =, of an inch in diameter. Their walls are formed
of fine membrane, similar to that of the intercellular
passages, and continuous with it, which membrane is

Fig. 59.*

* Fig. 59. Two small groups of air-cells, or infundibula, a a, with
air-cells, 6 b, and the ultimate bronchial tubes, ¢ c, with which the air-
cells communicate. From a new-born child (after Kélliker).

/

192 RESPIRATION.

folded on itself so as to form a sharp-edged border at
each circular orifice of communication between contiguous
air-cells, or between the cells and the ,bronchial passages.
Numerous fibres of elastic tissue are spread out between
contiguous air-cells, and many of these are attached to the
outer surface of the fine membrane of which each cell is
composed, imparting to it additional strength, and the
power of recoil after distension (fig. 60, b and c), The

Fig. 60.*

cells are lined by a layer of squamous or tessellated epithe-
lium, not provided with cilia. Outside the cells, a net-
work of pulmonary capillaries is spread out so densely
(fig. 61), that the interspaces or meshes are even narrower

* Fig. 60. Air-cells of lung, magnified 350 diameters. a, Epithelial
lining of the cells ; b, Fibres of elastic tissue ; c, Delicate membrane of
which the cell-wall is construeted with elastic fibres attached to it (after.
Killiker). |

—_ ee

STRUCTURE OF THE LUNGS. 193

than the vessels, which are, on an average, -,!,5 of an
inch in diameter. Between the atmospheric air in the
cells and the blood in these vessels, nothing intervenes
but the thin membranes of the cells and capillaries and
the delicate epithelial lining of the former; and the
exposure of the blood to the air is the more complete,
because the folds of membrane between contiguous cells,
and often the spaces between the walls of the same, con-
tain only a single layer of capillaries, both sides of which
are thus at once exposed to the air.

The cells situated nearest to the centre of the lung are
smaller, and their networks of capillaries are closer than
those nearer to the circumference, in adaptation to the

more ready supply of fresh air to the central than the
peripheral portion of the lungs. The cells of adjacent
lobules do not communicate ; and those of the same lobule,
or proceeding from the same intercellular passage, do so
as a general rule only near angles of bifurcation; so that,

“ Fig. 61. Capillary net-work of the pulmonary blood-vessels in the
human lung (from Kélliker) &9. |
)

194 RESPIRATION,

when any bronchial tube is closed or obstructed, the
supply of air is lost for all the cells opening into it or its.

_ branches. — .

Mechanism of Respiration.

For the proper understanding of the mechanism by
which air enters and is expelled from the lungs, the follow-
ing facts must be borne in mind :—

The lungs form two distinct hollow bags (communicating -
with the exterior through the trachea and larynx), and are
always closely in contact with the inner surface of the
chest-walls, while their lower portions are closely in con-
tact with the diaphragm, or muscular partition which
separates the chest from the abdomen (figs. 31 and 65). The
lungs follow all movements of the parts in contact with them ;
and for the evident reason that the outer surface of the
lung-bag not being exposed directly to atmospheric pres-
sure, while the inner surface is so exposed, the pressure
from within preserves the lungs in close contact with the
parts surrounding them, and obliterates, practically, the
pleural space, and must continue to do so, until from some
cause or, other—say from an opening for the admission of
air through the chest-walls, the pressure on the outside of
the lung equals or exceeds that on the interior. Any such
artificial condition of things, however, need not here be
considered,

For the inspiration of air into the lungs it will be evi-
dent from the foregoing facts, that all that is necessary is
such a movement of the side-walls or floor of the chest, or
of both, that the capacity of the interior shall be enlarged.
By such increase of capacity there will be of course a
diminution of the pressure of the air in the lungs, and a
fresh quantity will enter through the larynx and trachea
to equalise the pressure on the inside and outside of the
chest. For the expiration of air, on the other hand,
it is also evident, that, by an opposite movement which

MECHANISM OF RESPIRATION. | 195

‘shall contract the capacity of the chest, the pressure in the
interior will be increased, and air will be expelled, until
the pressures within and without the chest are again
equal. In both cases the air passes through the trachea
and larynx, whether in entering or leaving the lungs,
there being no other communication with the exterior, and
the lung, for the reason before mentioned, remains under
all the circumstances described, closely in contact with the
walls and floor of the chest. To speak of expansion of the
-chest, is to speak also of expansion of the lung.

We have now to consider the means by which the chest-
eavity is alternately enlarged and contracted for the en-
trance and expulsion of atmospheric air; or, in technical
‘terms, for inspiration and expiration.

Respiratory Movements,

The chest is a cavity filled by the lungs, heart, and large

_ blood-vessels, etc., and closed everywhere against the en-

trance of air except by the way of the larynx and trachea.

It is bounded behind and at the sides by the spine and

ribs, and instront by the sternum and cartilages of the ribs.
Its floor is formed mainly by the diaphragm.

The immediate inner lining of all these parts is the
outer or polished layer of the pleura; and this membrane
also is stretched continuously across the top of the chest-
‘cavity, and mainly forms its roof.

The enlargement of the capacity of the chest in inspira- |

tion is a muscular act; the muscles concerned in producing
the effect being chiefly the diaphragm and the external
intercostal muscles, with that part of the internav inter-
costal which is between the cartilages of the ribs. These
‘are assisted by the levatores costarum, the serratus posticus
‘Superior, and some others.

The vertical diameter of the chest is inereased by the
contraction and consequent descent of the diaphragm,—
the sides of the muscle descending most, and the central

0 2

a

196 © RESPIRATION,

tendon remaining comparatively unmoved while the in-
tercostal, and other muscles just mentioned, by acting at

the same time, not only prevent the diaphragm during its.

contraction from drawing in the sides of the chest, but
increase the diameter of the chest in the Jateral direction,

by elevating the ribs; that is to say, by rotating them, to:
speak roughly, around an axis passing through their

sternal and spinal attachments,—somewhat after the
fashion of raising the handle of a bucket (fig. 62). This
is not all, however. Another effect of the contraction of

the intercostal muscles is to increase the antero-posterior

Fig. 62.

diameter of the chest,—by partially straightening out the
angle between the rib and its cartilage, and thus lengthen-
ing the distance between its spinal and sternal attachments.
(fig. 62, A). In this way, at the same time that the ribs
are raised, the sternum is pushed forward. This forward
movement of the sternum, which is accompanied by a

‘slight upward movement, isin part accomplished also by a

raising of the anterior extremities of the rib cartilages,
which of course, in any movement, carry the sternum with
them. The differences in shape and direction of the upper
and lower true ribs, and the more acute angles formed by

meth

RESPIRATORY MOVEMENTS, 197

the junction of the latter with their cartilages, make the
effect much greater at the lower than at the upper part of
ithe chest. Lee

Fig. 64.¢

The expansion of the chest in inspiration presents some

* Fig. 63 (after Hutchinson), The changes of the thoracic and
-abdominal walls of the male during respiration. The back is supposed
to be fixed in order to throw forward the respiratory movement as much
as possible. The outer black continuous line in front represents the
-ordinary breathing movement: the anterior margin of it being the
boundary of inspiration, the posterior margin the limit of expiration.
‘The line is thicker over the abdomen, since the ordinary respiratory
movement is chiefly abdominal : thin over the chest, for there is less
movement over that region. The dotted line indicates the movement
-on deep inspiration, during which the sternum advances while the
abdomen recedes,

+ Fig. 64 (after Hutchinson). The respiratory movement in the female.
The lines indicate the same changes asin the last figure. The thickness
-of the continuous line over the sternum shows the larger extent of the
‘ordinary breathing movement over that region in the female than in
‘the male,

198 RESPIRATION.

peculiarities in different persons and circumstances. In

young children, it is effected almost entirely by the dia-

phragm, which being highly arched in expiration, becomes:

flatter as it contracts, and, descending, presses on the

abdominal viscera, and pushes forward the front walls of”
the abdomen. The movement of the abdominal walls.
being here more manifest than that of any other part, it is-
usual to call this the abdominal mode or type of respiration. .

In adult men, together with the descent of the diaphragm,
and the pushing forward of the front wall of the abdomen,

the lower part of the chest and the sternum are subject to-
a wide movement in inspiration. In women, the move--

ment appears less extensive in the lower, and more ‘so in
the upper, part of the chest; a mode of breathing to which
a greater mobility of the first rib is adapted, and which

may have for its object the provision of sufficient space for~

respiration when the lower part of the chest is encroached
upon by the pregnant uterus. MM. Beau ‘and Maissiat

call the former the inferior costal, and the latter the superior

costal, type of respiration; but the annexed diagrams will
explain the difference better than the names will, for these
imply a greater diversity than naturally exists in the
modes of inspiration.

From the enlargement produced in inspiration, the chest

and lungs return in ordinary tranquil expiration, by t their -
elasticity ; the force employed by the inspiratory muscles in
distending the chest and overcoming the elastic resistance -
of the lungs and chest-walls, being returned as an expira--
tory effort when the muscles are relaxed. This elastic:

recoil of the rib-cartilages, but also of the lungs them-
selves, in consequence of the elastic tissue which they

contain in considerable quantity, is sufficient, in ordinary.
quiet breathing, to expel air from the chest in the intervals .
of inspiration, and no muscular power is required. In all:
voluntary expiratory efforts, however, as in speaking,
singing, blowing, and the like, and in many involuntary:

Pint -7

ee See a ee how al

ELASTIC RECOIL OF LUNGS AND CHEST. 199

actions also, as sneezing, coughing, etc., something more
than merely passive elastic power is of course necessary,
and the proper expiratory muscles are brought into action.
By far the chief of these are the abdominal muscles, which,
by pressing on the viscera of the abdomen, push up the
floor of the chest formed by the diaphragm, and by thus
making pressure on the lungs, expel air from them through
the trachea and larynx. All muscles, however, which de-
press the ribs, must act also as muscles of expiration, and
therefore we must conclude that the abdominal muscles are
assisted in their action by the greater part of the internal
intercostals, the triangularis sterni, the serratus posticus
inferior, etc. When by the efforts of the expiratory muscles,
the chest has been squeezed to less than its average dia-
meter, it again, on relaxation of the muscles, returns to
the normal dimensions by virtue of its elasticity. The
construction of the chest-walls, therefore, admirably adapts
them for recoiling against and resisting as well undue con-
traction as undue dilatation.

As before mentioned, the lungs, after distension in the
act of inspiration, contract by virtue of the elastic tissue
which is present in the bronchial tubes, on and between
the air-cells, and in the investing pleura. But in the
natural condition of the parts, they can never contract to
the utmost, but are always more or less “on the stretch,”
being kept closely in contact with the inner surface of the
walls of the chest by atmospheric pressure, able to act only
on their interior, and can contract away from these only
when, by some means or other, as by making an opening
into the pleural cavity, or by the effusion of fluid there, the
pressure on the exterior and interior of the lungs becomes
equal. Thus, under ordinary circumstances, the degree of
contraction or dilatation of the lungs is dependent on that
_ of the boundary walls of the chest, the outer surface of the
one being in close contact with the inner surface of the
other, and obliged to follow it in all its movements.

——

200 RESPIRATION,

Respiratory Rhythm. :

The acts of expansion and contraction of the chest, take ~

up, under ordinary circumstances, a nearly equal time, and
can scarcely be said to be separated from each other by an
intervening pause.

The act of inspiring air, however, especially in women
and children, is a little shorter than that of expelling it,
and there is commonly a very slight pause between the end
of expiration and the beginning of the next inspiration.
The respiratory rhythm may be thus expressed :—

Inspiration ‘ ‘ ‘ ; 6
Expiration . ; Song 7 or 8
A very slight pause. |

Respiratory Movements of the Glottis.

During the action of the muscles which directly draw
air into the chest, those which guard the opening through
which it enters are not passive. In hurried breathing the
instinctive dilatation of the nostrils is well seen, although
under ordinary conditions it may not be noticeable. The
opening at the upper part of the larynx, however, or rima
glottidis (fig. 65), is dilated at each inspiration, for the
more ready passage of air, and collapses somewhat at each
expiration, its condition, therefore, corresponding during
respiration with that of the walls of the chest. There is a
further likeness between the two acts in that, under ordi-
nary circumstances, the dilatation of the rima glottidis is a
muscular act, and its contraction chiefly an elastic recoil;
although, under various conditions, to be hereafter men-
tioned, there may be, in the contraction of the glottis, con-
siderable muscular power exercised.

wee eS ee

QUANTITY OF AIR RESPIRED. 201

Quantity of Air Respired.

The quantity of air that is changed in the lungs in each
act of ordinary tranquil breathing is variable, and is very
difficult to estimate, because it is hardly possible to breathe
naturally while, as in an experiment, one is attending to
the process. Probably 30 to 35 cubic inches are a fair

average in the case of healthy young and middle-aged |

men; but Bourgery is perhaps right in saying that old
people, even in health, habitually breathe more deeply,
and change in each respiration a larger quantity of air
than younger persons do. ;

The total quantity of air which passes into and out of
the lungs of an adult, at rest, in 24 hours, has been esti-
mated by Dr. E. Smith at about 686,000 cubic inches.
This quantity, however, is largely increased by exertion ;
and the same observer has computed the average amount
for a hard-working labourer in the same time, at 1,568,390
cubic inches.

The quantity which is habitually and almost uniformly
changed in euch act of breathing, is called by Mr. Hutchin-
son, breathing air. The quantity over and above this which
a man can draw into the lungs in the deepest inspiration,
he names complemental air: its amount is various, as will
be presently shown. After ordinary expiration, such as
that which expels the breathing air, a certain quantity of
air remains in the lungs, which may be expelled by a
forcible and deeper expiration: this he terms reserve air.
But, even after the most violent expiratory effort, the
lungs are not completely emptied; a certain quantity
always remains in them, over which there is no voluntary

control, and which may be called residual air. Its amount .

depends in great measure on the absolute size of the chest,
and has been variously estimated at from forty to two
hundred and sixty cubic inches.

The greatest respiratory capacity of the chest is indi-

202 _ RESPIRATION.

cated by the quantity of air which a person can expel from
his lungs by a forcible expiration after the deepest inspi-
ration that he can make. Mr. Hutchinson names this the
vital capacity: it expresses the power which a person has
of breathing in the emergencies of active exercise, violence,
and disease; and in healthy men it varies according to
stature, weight, and age.

It is found by Mr. Hutchinson, from whom most of our
ie information on this subject is derived, that at a tempera-
c Ac “ture of 60° F., 22 225 cubic inches is the averate vital capacity

uf /4of a ealike satan, ‘five feet seven inches in height. For
every inch of height above this standard the capacity is
increased, on an average, by eight cubic inches; and for
every inch below, it is diminished by the same amount.
This relation of capacity to height is quite independent of
the absolute capacity of the cavity of the chest; for the
cubic contents of the chest do not always, or even gener-
ally, increase with the stature of the body; and a person
of small absolute capacity of chest may have a large capacity
of respiration, and vice.versé. The capacity of respiration is
determined only by the mobility of the walls of the chest;
but why this mobility should increase in a definite ratio
with the height of the body is yet unexplained, and must
be difficult of solution, seeing that the height of the body
is chiefly determined by that of the legs, and not by the
height of the trunk or the depth of the chest. But the vast
number of observations made by Mr. Hutchinson seem to
leave no doubt of the fact as stated above.

The influence of weight on the capacity of respiration is
less manifest and considerable than that of height: and it
is difficult to arrive at any definite conclusions on this
point, because the natural average weight of a healthy
man in relation to stature has not yet been determined.
As a general statement, however, it may be said that the
capacity of respiration is not affected by weights under
161 pounds, or 114 stones; but that, above this point, it

QUANTITY OF AIR. RESPIRED. 203.

is diminished at the rate of one cubic inch for every addi-
tional pound up to 196 pounds, or 14 stones; so that, for
example, while a man of five feet six inches, and weighing
less than 114 stones, should be able to expire 217 cubic
inches, one of the same height, weighing 124 stones, might
expire only 203 cubic inches.

By age, the capacity appears to be increased from about
the fifteenth to the thirty-fifth year, at the rate of five
cubic inches per year, from thirty-five to sixty-five it
diminishes at the rate of about one and a-half cubic inch
per year; so that the capacity of respiration of a man of
sixty years old would be about 30 cubic inches less than
that of a man forty years old, of the same height and
weight.

Mr. Hutchinson’s observations were made almost exclu-
sively on men; and his conclusions are, perhaps, true of
them alone; for women, according to Bourgery, have only
_half the capacity of breathing that men of the same age
have, Nee

The number of respirations in a healthy adult person
usually ranges from fourteen to eighteen per minute.

It is greater in infancy and childhood; and of course
varies much according to different circumstances, such as
exercise or rest, health or disease, etc. Variations in the
number of respirations correspond ordinarily with similar
variations in the pulsations of the heart. In health the

proportion is about I to 4, or I to 5, and when the |
rapidity of the heart’s action is increased, that of the chest. —

movement is commonly increased also; but not in every
case in equal proportion. It happens occasionally in
disease, especially of the lungs or air-passages, that the
number of respiratory acts increases in quicker proportion
than the beats of the pulse; and, in other affections, much
more commonly, that the number of the pulses is greater
in proportion than that of the respirations.

According to Mr. Hutchinson, the force with which the

f
44
Hy

4
:
és

bow

204 _- RESPIRATION.

inspiratory muscles are capable of acting, is greatest in
individuals of the height of from five feet. seven inches to

five feet eight inches, and will elevate a column of three —

inches of mercury. Above this height, the force decreases
as the stature increases; so that the average of men of six
feet can elevate only about two and a half inches of mer-
cury. The force manifested in the strongest expiratory
acts is, on the average, one-third greater than that exer-
cised in inspiration. But this difference is in great
measure due to the power exerted by the elastic reaction of
the walls of the chest; and it is also much influenced by
the disproportionate strength which the expiratory muscles
attain, from their being called into use for other purposes
than that of simple expiration. The force of the inspira-
tory act is, therefore, better adapted than that of the
expiratory for testing the muscular strength of the body.

The following table expresses the result of numerous
experiments by Mr. Hutchinson on this subject, the instru-
ment used to gauge the inspiratory and expiratory power
being a hemadynamometer (see p. fo), to which was
attached a tube ; fitting the nostrils, and through which the
inspiratory or expiratory effort was made :—

Power of Power of

Inspiratory Muscles. Exp’ ratory Muscles.
1°5 in. . Weak 4 4 . 2°Oin,
20... . - Ordinary .. Semi i 5
2°5 aa 4 . Strong. ‘ :. Seas
3°5 Sh . . Very strong. ie hag ee,

AK typ lab . Remarkable. ni? 5 Bid
5°5 » .. Veryremarkable. . 7°0,,
Gr) Fo. . Extraordinary . (Six
705 . . Very extraordinary . 10°0 ,,

Mr. Hutchinson remarks :—‘‘ Suppose a man to lift by
his inspiratory muscles three inches of mercury, what
muscular effort has he used? The mere quantity of fluid
lifted may be very inconsiderable (and as such, I have
found men wonder they could not elevate more), but not

QUANTITY OF AIR RESPIRED. 205

so the power exerted, when we recollect that hydrostatic
law, which Mr. Bramah adopted to the construction of a
very convenient press. To apply this law here, the
- diaphragm alone must act under such an effort, with a
force equal to the weight of a column of mercury 3 inches
in height, and whose base is commensurate to the area of
the diaphragm. The area of the base of one of the chests
now before the Society, is 57 square inches; therefore, had
this man raised 3 inches of mercury by his inspiratory
muscles, his diaphragm alone in this act must have
opposed a resistance equal to more than 23 oz. on every
inch of that muscle, and a total weight of more than 83 lbs.
Moreover, the sides of his chest would resist a pressure from
the atmosphere equal to the weight of a covering of mer-
cury three inches in thickness, or more than 23 oz. on every
inch surface, which, if we take at 318 square inches, the
chest will be found resisting a pressure of 731 lbs.; and

allowing the elastic resistance of the ribs as 14 inch of

‘mercury, this will bring the weight resisted by the chest
as follows :—

Diaphragm «ly : : ac 2 OS ba.

Walls of the chest ; y Fates al % 4 ae

Elastic foree . ; ; : See 4 te
Total ‘ ‘ < * 5 3046. ,,

“In round numbers it may be said, that the parietes
of the thorax resisted 1000 lbs. of atmospheric pressure,

and tiat not counterbalanced,—to say nothing of the / fi

elastic power of the lungs, which co-operated with this
pressure.

“J would not venture at present to state exactly the
distribution of muscular fibre over the thorax, which is
called into action when resisting this 1046 lbs., but I think
I am safe in stating that nine-tenths of the thoracic sur-
face conspire to this act.

‘‘What is here said of the muscular part of the chest

. al es

206 RESPIRATION.

resisting such a force, must not be confounded with a former
statement of ‘two-thirds being lifted by the inspiratory
muscles, and one-third left dormant,’ under a force equal
to 301 lbs. In this case the 301 lbs. are lifted; in the
other, nine-tenths of 1046 lbs. are said to be resisted.

“The glass receiver of an air-pump may resist 15 lbs. on
the square inch; yet it may be said to lift nothing. This
question of the thoracic muscular force and resistance, and
muscular distribution, is rendered complicate by the pre-
sence of so much osseous matter entering into the composi-
tion of the chest, which can scarcely be considered to act
the same as muscle.”

The great force of the inspiratory efforts during apnoea
was well shown in some of the experiments performed by
the Medico-Chirurgical Society’s Committee on Suspended
Animation. On inserting a glass tube into the trachea of
a dog, and immersing the other end of the tube in a vessel
' of mercury, the respiratory efforts during apnoea were so
great as to draw the mercury four inches up the tube.
The influence of the same force was shown in other expe-
riments, in which the heads of animals were immersed
both in mercury and in liquid plaster of Paris. In both
cases the material was found, after death, to have been
drawn up into all the bronchial tubes, filling the tissue of
the lungs.

Much of the force exerted in inspiration is employed in
overcoming the resistance offered by the elasticity of the
walls of the chest and of the lungs. Mr. Hutchinson esti-
mated the amount of this elastic resistance, by observing
the elevation of a column of mercury raised by the return
of air forced, after death, into the lungs, in quantity equal
to the known capacity of respiration during life; and he
calculated that, in a man capable of breathing 200 cubie
inches of air, the muscular power expended upon the elas-
ticity of the walls of the chest, in making the deepest
inspiration, would be equal to the raising of at least

VITAL CAPACITY. 207

301 pounds avoirdupois. To this must be added about
150 lbs. for the elastic resistance of the lungs themselves,
so that the total force to be overcome by the muscles in
the act of inspiring 200 cubic inches of air is more than
450 lbs.

In tranquil respiration, supposing the amount of breath-
ing air [to be twenty cubic inches, the resistance of the
walls of the chest would be equal to lifting more than
100 pounds; and to this must be added about 70 pounds
for the elasticity of the lungs. The elastic force overcome
im ordinary inspiration must, therefore, be equal to about
170 pounds.

It is probable, that in the quiet ordinary respiration,
which is performed without consciousness or effort of the
will, the only forces engaged are those of the inspiratory
muscles, and the elasticity of the walls of the chest and
the lungs. It is not known under what circumstances the
contractile power which the bronchial tubes possess, by
means of their organic muscular fibres, is brought into
action. It is possible, as Dr. R. Hall maintained, that
it may exist in expiration; but it is more likely that
its chief purpose is to regulate and adapt, in some measure,
the quantity of air admitted to the lungs, and to each part
of them, according to the supply of blood. Another pur-
pose probably served by the muscular fibres of the bron-
chial tubes is that of contracting upon and gradually ex- |
pelling collections of mucus, which may have accumulated —
within the tubes; and cannot be ejected by forced expiratory |
efforts, owing to collapse or other morbid conditions of |
the portion of lung proceeding from the obstructed tubes
(Gairdner).

The muscular action in the lungs, morbidly excited, is
probably the chief cause of the phenomena of spasmodic
asthma. It may be demonstrated by galvanizing the lungs
shortly after taking them from the body, Under such a
stimulus, they contract so as to lift up water placed ina

<_ —"

208. RESPIRATION.

tube introduced into the trachea (C. J. B. Williams); and
Volkmann has shown that they may be made to contract by
stimulating their nerves. He tied a glass tube, drawn
fine at one end, into the trachea of a beheaded animal;
and when the small end was turned to the flame of a
candle, he galvanised the pneumogastric trunk. Each
time he did so the flame was blown, and once it was
blown out.

The changes of the air in the lungs effected by these
respiratory movements are assisted by the various con-
ditions of the air itself. According to the law observed in
the diffusion of gases, the carbonic acid evolved in the air-
cells will, independently of any respiratory movement,
tend to leave the lungs, by diffusing itself into the external
air, where it exists in less proportion; and according to
the same law, the oxygen of the atmospheric air will tend
of itself towards the air-cells in which its proportion is
less than it is in the air in the bronchial tubes or in that
external to the body. But for this tendency in the oxygen
and carbonic acid to mix uniformly, within and without
the lungs, the reserve and residual air would, probably,
be very injuriously charged with carbonic acid; for the
respiratory movements alone are not enough to empty
the air-cells, and perhaps expel only the air which lies
in the larger bronchial tubes. Probably also the change
is assisted by the different temperature of the air
within and without the lungs; and by the action of the
cilia on the mucous membrane of the bronchial tubes,

the continual vibrations of which may serve to prevent. |
the adhesion of the air to the moist surface of the mem- —

brane.

Movement of Blood in the Respiratory Organs.

To be exposed to the air thus alternately moved into and

out of the air-cells and minute bronchial tubes, the blood is _

propelled from the right ventricle through the pulmonary

ee Pe torts Ye “i a StF

CONTRACTION OF BRONCHI. 209

capillaries in steady streams, and slowly enough to permit
every minute portion of it to be for a few seconds exposed
to the air, with only the thin walls of the capillary vessels
and air-cells intervening. The pulmonary circulation is
of the simplest kind: for the pulmonary artery branches
regularly ; its successive branches run in straight lines,
and do not anastomose; the capillary plexus is uniformly
spread over the air-cells and intercellular passages; and
the veins derived from it proceed in a course as simple and
uniform as that of the arteries, their branches converging
but not anastomosing. The veins have no valves, or only
small imperfect ones prolonged from their angles of junc-
tion, and incapable of closing the orifice of either of the
veins between which they are placed. The pulmonary cir-
culation also is unaffected by changes of atmospheric
pressure, and is not exposed to the influence of the pressure
of muscles: the force by which it is accomplished, and the |
course of the blood are alike simple.

The blood which is conveyed to the lungs by the pul-
monary arteries is distributed to these organs to be purified
and made fit for the nutrition of all other parts of the
body. The capillaries of the pulmonary vessels are ar-
ranged solely with reference to this object, and therefore
can have but little to do with the nutrition of the lungs ;
or at least, only of those portions of the lungs with which
they are in intimate connection for another purpose. For
the nutrition of the rest of the lungs, including the pleura,
interlobular tissue, bronchial tubes and glands, and the
walls of the larger blood vessels, a special supply of arterial
blood is furnished through one or two bronchial arteries,
the branches of which ramify in all these parts. The blood
of the bronchial artery, when, having served for the nutri-
tion of these parts, it has become venous, is carried partly
into the branches of the bronchial vein, and thence to the
right auricle, and partly into the small branches of the

pulmonary artery, or, more directly, into the pulmonary
Bc

210 RESPIRATION.

capillaries, whence, being with the rest of the blood arte-
rialized, it is carried to the pulmonary veins and left side
of the heart.

Changes of the Air in Respiration.

By their contact in the lungs the composition of both air
and blood is changed. The alterations of the former being
manifest, simpler than those of the latter, and in some
degree illustrative of them, may be considered first.

The atmosphere we breathe has, in every situation in
which it has been examined in its natural state, a nearly
uniform composition. It is a mixture of oxygen, nitrogen,
carbonic acid, and watery vapour, with, commonly, traces
of other gases, as ammonia, sulphuretted hydrogen, etc.
Of every 100 volumes of pure atmospheric air, 79 volumes
(on an average) consist of nitrogen, the remaining 21 of
_ oxygen. The~ proportion of carbonic acid is extremely
small; 10,000 volumes of atmospheric air contain only
about 4 or 5 of carbonic acid.

The quantity of watery vapour varies greatly, according
to the temperature and other circumstances, but the at-
mosphere is never without some. In this country, the
average quantity of watery vapour in the atmosphere is
1°40 per cent.

The changes produced by respiration on the atmospherie
air are, that, 1, it is warmed; 2, its carbonic acid is in-
creased ; 3, its oxygen is diminished; 4, its watery vapour
is increased; 5, a minute amount of organic matter and of
free ammonia is added to it.

1. The expired air, heated by its. contact with the in-
terior of the lungs, is (at least in most climates) hotter
than the inspired air. Its temperature varies between 97°
and 993°, the lower temperature being observed when
the air has remained but a short time in the lungs, rather
than when it is inhaled at a very low temperature ; for
whatever the temperature when inhaled may be, the air

NPA I ORAS

Sey ve

PCIE

CHANGES OF AIR IN RESPIRATION. 2If

nearly acquires that of the blood before it is expelled from
the chest.

2. The carbonic acid in respired air is always increased ;
but the quantity exhaled in a given time is subject to
change from various circumstances. From every volume
of air inspired, about 44 per cent. of oxygen are abstracted ;
while a rather smaller quantity of carbonic acid is added
in its place, It may be stated, as a general average
deduced from the results of experiments by Valentin and
Brunner, that, under ordinary circumstances, the quantity
of carbonic acid exhaled into the air breathed by a healthy
adult man amounts to 1346 cubic inches, or about 636
grains per hour. According to this estimate, which cor-
responds very closely with the one furnished by Sir H.
Davy, and does not widely differ from those obtained by
Allen and Pepys, Lavoisier, and Dr, Ed. Smith, the weight
of carbon excreted from the lungs is about 173 grains per
hour, or rather more than 8 ounces in the course of twenty-
four hours. Discrepancies in the results obtained by
different experimenters may be due to the variations to
which the exhalation of carbonic acid is liable in different
circumstances; for even in health the quantity varies accord-
ing to age, sex, diversities in the respiratory movements,

external temperature, the degree of purity of the respired

air, and other circumstances. Each of these deserves a
brief notice, because it affords evidence concerning either
the sources of carbonic acid exhaled, or the mode in which
it is separated from the blood.

a. Influence of Age and Sex.—According to Andral and
Gavarret the quantity of carbonic acid exhaled into the
air breathed by males, regularly increases from eight to
thirty years of age; from thirty to forty it is stationary
or diminishes a little; from forty to fifty the diminution is
greater ; and from fifty to extreme age it goes on diminish-
ing, till it scarcely exceeds the quantity exhaled at ten

years old. In females (in whom the quantity exhaled is
P 2

212 RESPIRATION.

always less than in males of the same age) the same
regular increase in quantity goes on from the eighth year
to the age of puberty, when the quantity abruptly ceases
to increase, and remains stationary so long as they con-
tinue to menstruate. When, however, menstruation has
ceased, either in advancing years or in pregnancy, or
morbid amenorrhea, the exhalation of carbonic acid again
augments; but when menstruation ceases naturally, it
soon decreases again at the same rate that it does in
old men.

b. Influence of Respiratory Movements.—According to
Vierordt, the more quickly the movements of respiration
are performed, the smaller is the proportionate quantity
of carbonic acid contained in each volume of the expired
air. Thus he found that, with six respirations per minute,
the quantity of expired carbonic acid was 5°528 per cent. ;
with twelve respirations, 4°262 per cent.; with twenty-
four, 3°355; with forty-eight, 2-984; and with ninety-six,
2°662. Although, however, the proportionate quantity of
carbonic acid is thus ‘diminished during frequent respira-
tion, yet the absolute amount exhaled into the air within
a given time is increased thereby, owing to the larger
quantity of air which is breathed in the time. This is
the case, whether the respiration be voluntarily accelerated,
or naturally increased in frequency, as it is after feeding,
active exercise, etc. By diminishing the frequency, and
increasing the depth of respiration, the per-centage pro
portion of carbonic acid in the expired air is diminished ;
being in the deepest respiration as much as 1°97 per cent.
less than in ordinary breathing. But for this proportionate
diminution also, there is a full compensation in the greater
total volume of air which is thus breathed. Finally, the
last half of a volume of expired air contains more carbonic
acid than the half first expired; a circumstance which is
explained by the one portion of air coming from the
remote part of the lungs, where it has been in more

2 Sas Pa

INFLUENCE OF TEMPERATURE AND SEASON. 213

immediate and prolonged contact with the blood than the
other has, which comes chiefly from the larger bronchial
tubes.

c. Influence of external Temperature.—The observations
made by Vierordt at various temperatures between 38° F.
and 75° F, show, for warm-blooded animals, that within
this range, every rise equal to 10° F. causes a diminution
of about two cubic inches in the- quantity of carbonic
acid exhaled per minute. Letellier, from experiments
performed on animals at much higher and lower tempera-
tures than the above, also found that the higher the tempe-
rature of the respired air (as far as 104° F.), the less is the
amount of carbonic aid exhaled into it, whilst the nearer
it approaches zero the more does the carbonic acid increase.
The greatest quantity exhaled at the lower temperatures he
found to be about twice as much as the smallest exhaled at
the higher temperatures.

da. Season of the Year.—Dr. Edward Smith has shown
that the season of the year, independently of temperature,
also materially influences the respiratory phenomena; for
with the same cemperature, at different seasons, there is a
great diversity in the amount of carbonic acid expired.
According to his observations, spring is the season of the
greatest, and autumn of the least activity of the respiratory
and other functions.

e. Purity of the Respired Air.—The average quantity of
carbonic acid given out by the lungs constitutes about 4°48
per cent. of the expired air; but if the air which is breathed
be previously impregnated with carbonic acid (as is the case
when the same air is frequently respired), then the quantity
of carbonic acid exhaled becomes much less. This is
shown by the results of two experiments performed by
Allen and Pepys. In one, in which fresh air was taken in
at each respiration, thirty-two cubic inches of carbonic acid
were exhaled in a minute; whilst in the other, in which the
same air was respired repeatedly, the quantity of carbonic

214 RESPIRATION.

acid emitted in the same time was only 9°5 cubic inches.
They found also that, however often the same air may be
respired, even if until it will no longer sustain life, it does
not become charged with more than ten per cent. of carbonic
acid. The necessity of a constant supply of fresh air, by
means of ventilation, through rooms in which many persons
are breathing together, or in which, from any other source,
much carbonic acid is evolved, is thus rendered obvious ;
for even when the air is not completely irrespirable, yet in
the same proportion as it is already charged with carbonic
acid, does the further extrication of that gas from the lungs
suffer hindrance.

f. Hygrometric State of Atmosphere.—Lehmann’s observa-
tions have shown that the amount of carbonic acid exhaled
is considerably influenced by the degree of moisture of the
atmosphere, much more being given off when the air is
moist than when it is dry.

g. Period of the Day.—The period of day seems to exercise
a slight influence on the amount of carbonic acid exhaled
in a given time, though beyond the fact that the quantity
exhaled is much less by night, we are scarcely yet in a posi-
tion to state that variations in the amount exhaled occur at
uniform periods of the day, independently of the influence -
of other circumstances.

h. Food.—By the use of food the quantity is increased,
whilst by fasting it is diminished: and, according to Reg-
nault and Reiset, it is greater when animals are fed on fari-
naceous food than when fed on meat. Spirituous drinks,
especially when taken on an empty stomach, are generally
believed to produce an immediate and marked diminution
in the quantity of this gas exhaled. Recent observations
by Dr. Edward Smith, however, furnish some singular re-
sults on this subject. Dr. Smith found, for example, that
the effects produced by spirituous drinks depend much on
the kind of drink taken. Pure alcohol tended rather to
increase than to lessen respiratory changes, and the amount,

*
I
4

-EFFECTS OF EXERCISE AND SLEEP. 215

therefore, of carbonic acid expired: rum, ale, and porter,
also sherry, had very similar effects. On the other hand,
brandy, whisky and gin, particularly the latter, almost
always lessened the respiratory changes, and consequently
the amount of carbonic acid exhaled.

i. Exercise and Sleep,— Bodily exercise, in moderation, in-
creases the quantity to about one-third more than it is
during rest: and for about an hour after exercise, the volume
of the air expired in the minute is increased about 118
cubic inches: and the quantity of carbonic acid about 7°8
cubic inches per minute. Violent exercise, such as full
labour on the treadwheel, still further increases, according
to Dr. E. Smith, the amount of the acid exhaled.

During sleep, on the other hand, there is a considerable
diminution in the quantity of this gas evolved ; a result pro-
bably in great measure dependent on the tranquillity of
breathing: directly after walking, there is a great, though
quickly transitory, increase in the amount exhaled. A
larger quantity is exhaled when the barometer is low than
when it is high.

3. The Oxygen in respired Air is always less than in the
same air before respiration, and its diminution is generally
proportionate to the increase of the carbonic acid. The
experiments of Valentin and Brunner -seem to show, that,
for every volume of carbonic acid exhaled into the air,
1°I17421 volumes of oxygen are absorbed from it: and
that when the average quantity of carbonic acid, i.¢., 1346
cubic inches, or 636 grains, is exhaled in the hour, the
quantity of oxygen absorbed in the same time is 1584 cubic
inches or 542 grains. According to this estimate, there is
more oxygen absorbed than is exhaled with carbon to form
carbonic acid without change of volume; and to this general
conclusion, namely, that the volume of air expired in a
given time is less than that of the air inspired (allowance
being made for the expansion in being heated), and that
the loss is due to a portion of oxygen absorbed and not

216 RESPIRATION.

returned in the exhaled carbonic acid, all observers agree,
though as to the actual quantity of oxygen so absorbed
they differ even widely.

The quantity of oxygen that does not combine with the
carbon given off in carbonic acid from the lungs, is probably
disposed of in forming some of the carbonic acid and water
given off from the skin, and in combining with sulphur and
phosphorus to form part of the acids of the sulphates and
phosphates excreted in the urine, and probably also, from
the experiments of Dr. Bence Jones, with the nitrogen of
the decomposing nitrogenous tissues.

The quantity of oxygen consumed seems to vary much,
not only in different individuals, but in the same individual
at different periods; thus it is considerably influenced by
food, being greater in dogs when fed on farinaceous than
on animal food, and much diminished during fasting, while
it varies at different stages of digestion. Animals of small
size consume a relatively much greater amount of oxygen
than larger ones. The quantity of oxygen in the atmosphere
surrounding animals, appears to have very little influence
on the amount of this gas absorbed by them, for the quan-
tity consumed is not greater even though an excess of
oxygen be added to the atmosphere experimented with
(Regnault and Reiset)..

The Nitrogen of the Atmosphere, in relation to the respira-
tory process, is supposed to serve only mechanically, by
diluting the oxygen, and moderating its action upon the
system. This purpose, or the mode of expressing it, has
been denied by Liebig, on the ground that if we suppose
the nitrogen removed, the amount of oxygen in a given
space would not be altered. But, although it be true that,
if all the nitrogen of the atmosphere were removed and
not replaced by any other gas, the oxygen might still
extend over the whole space at present occupied by the
mixture of which the atmosphere is composed; yet since,
under ordinary circumstances, oxygen and nitrogen, when

EXHALATION OF WATERY VAPOUR, 217

mixed together in the ratio of one volume to four, produce
a mixture which occupies precisely five volumes, with all
the properties of atmospheric air, it must result that a
given volume of atmosphere drawn into the lungs con-
tains four-fifths less weight of oxygen than an equal
volume composed entirely of oxygen. The greater rapidity
and brilliancy with which combustion goes on in an atmo-
sphere of oxygen than in one of common air, and the
increased rapidity with which the ordinary effects of
respiration are produced when oxygen instead of atmo-
spheric air is breathed, seem to leave no doubt that the
nitrogen with which the oxygen of the atmosphere is
mixed has the effect of diluting this gas, in the same sense
and degree as one part of alcohol is diluted when mixed
with four parts of water.

It has been often discussed whether nitrogen is ever
absorbed by or exhaled from the lungs during respiration.

-At present, all that can be said on the subject is that,
under most circumstances, animals appear to expire a very
small quantity above that which exists in the inspired air.
‘During prolonged fasting, on the contrary, a small quantity
appears to be absorbed.

4. Watery Vapour is, under ordinary circumstances,
always exhaled from the lungs in breathing. The quan-
tity emitted is,‘as a general rule, sufficient to saturate the
expired air, or very nearly so. Its absolute amount is,
therefore, influenced by the following circumstances. First,
by the quantity of air respired; for the greater this is, the
greater also will be the quantity of moisture exhaled.
Secondly, by the quantity of watery vapour contained in
the air previous to its being inspired; because the greater
this is, the less will be the amount required to complete
the saturation of the air. Thirdly, by the temperature of
the expired air; for the higher this is, the greater will be
the quantity of watery vapour required to saturate the
air. Fourthly, by the length of time which each volume

218 RESPIRATION.

of inspired air is allowed to remain in the lungs; for it
seems probable that, although during ordinary respiration
the expired air is always saturated with watery vapour,
yet when respiration is performed very rapidly the air has
scarcely time to be raised to the highest temperature, or be
fully charged with moisture ere it is expelled.

For. ordinary cases, however, it may be held that the
expired air is saturated with watery vapour, and hence is
derivable a means of estimating the quantity exhaled in
any given time: namely, by subtracting the quantity con-
tained in the air inspired from the quantity which (at the
barometric pressure) would saturate the same air at the
temperature of expiration, which is ordinarily about 99°.
And, on the other hand, if the quantity of watery vapour
in the expired air be estimated, the quantity of air itself
may from it be determined, being as much as that quantity
of watery vapour would saturate at the ascertained tem-
perature and barometric pressure.

The quantity of water exhaled from the lungs in twenty-
four hours ranges (according to the various modifying cir-
cumstances already mentioned) from about 6 to 27 ounces,
the ordinary quantity being about 9 or 10 ounces. Some
of this is probably formed by the combination of the excess
of oxygen absorbed in the lungs with the hydrogen of the
blood; but the far larger proportion of it must be the mere
exhalation of the water of the blood, taking place from the
surfaces of the air-passages and cells, as it does from the
free surfaces of all moist animal membranes, particularly
at the high temperature of warm-blooded animals. It is
exhaled from the lungs whatever be the gas respired, con-
tinuing to be expelled even in hydrogen gas.

5. The Rev. J. B. Reade showed, some years ago, and
Dr. Richardson’s experiments confirm the fact, that am-
monia is among the ordinary constituents of expired air.
It seems probable, however, both from the fact that this
substance cannot be always detected, and from its minute

CHANGES IN BLOOD. 219

amount when present, that the whole of it may be derived
from decomposing particles of food left in the mouth, or
from carious teeth or the like; and that it is, therefore,
only an accidental constituent of expired air.

The quantity of organic matter in the breath has been
lately investigated by Dr. Ransome, who calculates that
about 3 grains are given on from the lungs of an adult in
twenty-four hours.

Changes produced in the Blood by Respiration.

The most obvious change which the blood undergoes in
its passage through the lungs is that of colour, the dark
crimson of venous blood being exchanged for the bright
scarlet of arterial blood. (The circumstances which have
been supposed to give rise to this change, the conditions
capable of effecting it independent of respiration, and some
other differences between arterial and venous blood, were
discussed in the chapter on Buoop, p. 85) :—2nd, and in
connection with the preceding change, it gains oxygen;
3rd, it loses carbonic acid; 4th, it becomes 1° or 2° F.
warmer; 5th, ic coagulates sooner and more firmly, and,
apparently, contains more fibrin.

The oxygen absorbed into the blood from the atmospheric
air in the lungs is combined chemically with the hemo-
globin of the red blood corpuscles. In this condition it is
carried in the arterial blood to the various parts of the
body, and with it is, in the capillary system of vessels,
brought into near relation or contact with the elementary
parts of the tissties. Herein co-operating probably in the
process of nutrition, or in the removal of disintegrated
parts of the tissues, a certain portion of the oxygen which
the arterial blood contains disappears, and a proportionate
quantity of carbonic acid and water is formed.

But it is not alone in the disintegrating processes to
which all parts of the body are liable, that oxygen is con-
sumed and carbonic acid and water are formed in its

220 RESPIRATION.

consumption. A like process occurs in the blood itself,
independently of the decay of the tissues; for on the
continuance of such chemical processes depend, directly
or indirectly, not only the temperature of the body, but
all the forces, the nervous, the muscular, and others,
manifested by the living organism.

The venous blood, containing the new-formed carbonic
acid, returns to the lungs, where a portion of the carbonic
acid is exhaled, and a fresh supply of oxygen is again
taken in.

“Mechanism of Various Respiratory Actions.

It will be well here, perhaps, to explain some respiratory
acts, which appear at first sight somewhat complicated,
but cease to be so when the mechanism by which they
are performed is clearly understood. The accompanying
diagram (fig. 65) shows that the cavity of the chest is
separated from that of the abdomen by the diaphragm,
which, when acting, will lessen its curve, and thus de-
scending, will push downwards and forwards the abdominal
viscera; while the abdominal muscles have the opposite
effect, and in acting will push the viscera upwards and
backward, and with them the diaphragm, supposing its
ascent to be not from any cause interfered with. From
the same diagram it will be seen that the lungs communi-
cate with the exterior of the body through the glottis, and
further on through the mouth and nostrils — through
either of them separately, or through both at the same
time, according to the position of the soft palate. . The
stomach communicates with the exterior of the body
through the cmsophagus, pharynx, and mouth; while
below, the rectum opens at the anus, and the bladder
through the urethra. All these openings, through which
the hollow viscera communicate with the exterior of the
body, are guarded by muscles, called sphincters, which can

MECHANISM OF RESPIRATORY ACTIONS. 221

act independently of eachother. The position of the latter
is indicated in the diagram.
Let us take Fig. 65.

first the simple
act of sighing.
In this case
there isarather
prolonged in-

Soft Palate - - 4 SE — Tongue
spiratory effort Phary nx -7e~)
by the dia- of Ay, ") Rimee Glotlicts's
phragm and / Sal SEN - trachea

other muscles
concerned in
inspiration ;
the air almost
noiselessly pas- Eta He \
sing in through \
the glottis, and Diaphragri-—
by the elastic
recoil of the
lungsand chest
walls, and pro-
bably also of
the abdominal : BON =< = aphhe Blediler
walls, being = :
rathersuddenly
expelled again.
Now, in the first, or inspiratory part of this act, the
descent of the diaphragm presses the abdominal viscera
downwards, and of course this pressure tends to evacuate
the contents of such as communicate with the exterior of
the body. Inasmuch, however, as their various openings
are guarded by sphincter muscles, in a state of constant
tonic contraction, there is no escape of their contents,
and air simply enters the lungs. In the second, or expira-
tory part of the act of sighing, there is also pressure made

a Dicefph reg tn

|- —Pylorees

tscles

| j SS
=

bdominc? Me

\ \
Intestines — ae =

A

-

222 RESPIRATION.

on the abdominal viscera in the opposite direction, by the
elastic or muscular recoil of the abdominal walls; but the
pressure is relieved by the escape of air through the open
glottis, and the relaxed diaphragm is pushed up again into
its original position. The sphincters of the stomach,
rectum, and bladder act as before.

Hiccough resembles sighing in that it is an inspiratory
act, but the inspiration is sudden instead of gradual, from
_ the diaphragm acting suddenly and spasmodically ; and the
air, therefore, suddenly rushing through the unprepared
rima glottidis, causes vibration of the vocal cords, and the
peculiar sound.

In the act of coughing, there is most often first an in-
spiration, and this is followed by an expiration; but when
the lungs have been filled by the preliminary inspiration,
instead of the air being easily let out again through
the glottis, the latter is momentarily closed by the
approximation of the vocal cords; and then the abdo-
minal muscles, strongly acting, push up the viscera
against the diaphragm, and thus make pressure on the
air in the lungs until its tension is sufficient to burst
open noisily the voeal cords which oppose its outward pas-
- sage. In this way a considerable force is exercised, and
mucus or any other matter that may need expulsion from
the lungs or trachea is quickly and sharply expelled by
the out-streaming current of air.

Now it is evident on reference to the diagram (fig. 65),
that pressure exercised by the abdominal muscles in the
act of coughing, acts as forcibly on the abdominal viscera
as on the lungs, inasmuch as the viscera form the medium
by which the upward pressure on the diaphragm is made,
and of necessity there is quite as great a tendency to the
expulsion of their contents as of the air in the lungs.
The instinctive and, if necessary, voluntarily increased
contraction of the sphincters, however, prevents any
escape at the openings guarded by them, and the pres-

ie.

COUGHING ; SNEEZING; VOMITING. - 223

sure is effective at one part only, eee the rima
glottidis.

The same remarks that dud to coughing, are almost
exactly applicable to the act of sneezing; but in this in-
stance the blast of air, on escaping from the lungs, is
directed by an instinctive contraction of the pillars of the
fauces and descent of the soft palate, chiefly through the
nose, and any offending matter is thence expelled.

In the act of vomiting, as in coughing, there is first an
inspiration; the glottis is then closed, and immediately
afterwards the abdominal muscles strongly act; but here
occurs the difference in the two actions. Instead of the
vocal cords yielding to the action of the abdominal mus-
cles, they remain tightly closed. Thus the diaphragm
being unable to go up, forms an unyielding surface against
which the stomach can be pressed. It is fixed, to use a
technical phrase. At the same time the cardiac sphincter
being relaxed while the pylorus is closed (see fig. 65), and
the stomach itself also contracting, the action of the abdo-
minal muscles, by these means assisted, expels the contents
of the organ through the cesophagus, pharynx, and mouth.
The reversed peristaltic action of the cesophagus probably
increases the effect.

In the act of voluntary expulsion of urine or feces,
there is first an inspiration, as in coughing, sneezing, and
vomiting; the glottis is then closed, and the diaphragm fixed
asin vomiting. Now, however, both the rima glottidis and
the cardiac opening of the stomach remain closed, and the
sphincter of the bladder or rectum, or of both, being re-
laxed, the evacuation of the contents of these viscera takes
place accordingly ; the effect being, of course, increased by
the muscular and elastic contraction of their own walls.
As before, there is as much tendency to the escape of
the contents of the lungs or stomach as of the rectum or
bladder; but the pressure is relieved only at the orifice,
the sphincter of which instinctively or involuntarily yields.

ld

_ ~ ES a

224 RESPIRATION.

In all these expulsive actions the diaphragm is quite |
passive; and when it is fied, it is in consequence of
the closure of the glottis (which by preventing the exit of
air from the lungs prevents its upward movement), not
from any exertion on its own part.

In females, during parturition, almost an exactly similar
action occurs, so far as the diaphragm and abdominal
walls are concerned, to that which takes place in a strain-
ing effort at expulsion of urine or feeces. The contraction
of the uterus, however, is both relatively and absolutely
more powerful than that of the bladder or rectum, although
it is greatly assisted by the inspiratory effort, by the fixing
of the diaphragm, and by the action of the abdominal
muscles, as in the other acts just described. In parturi-
tion, as in vomiting, the action of the abdominal muscles
is, to a great extent, involuntary—more so than it com-
monly is in the expulsion of feeces or urine; but in these
latter instances also, in cases of great pain and difficulty,
it may cease to be a voluntary act, and be quite beyond
the control of the will.

In speaking, there is a voluntary expulsion of air through
the glottis by means of the abdominal muscles; and the
vocal cords are put, by the muscles of the larynx, in a
proper position and state of tension for vibrating as the
air passes over them, and thus producing sound. The
sound is moulded into words by the tongue, teeth, lips,
etc.—the vocal cords producing the sound only, and having
nothing to do with articulation.

Singing resembles speaking in the manner: of its pro-
duction; the laryngeal muscles, by variously altering the
position and degree of tension of the vocal cords, pro-
ducing the different notes. Words used in the act of
singing are of course framed, as in speaking, by the
tongue, teeth, lips, etc.

Sniffing is produced by a somewhat quick action of the
diaphragm and other inspiratory muscles. The mouth is

SNIFFING ; SUCKING. — w35

however, closed, and by these means the whole stream of
air is made to enter by the nostrils. The ale nasi are,
commonly, at the same time, instinctively dilated.

Sucking is not properly a respiratory act, but it may be
most conveniently considered in this place. It is caused
chiefly by the depressor muscles of the os hyoides. These,
by drawing downwards and backwards the tongue and
floor of the mouth, produce a partial vacuum in the latter ;
_ and the weight of the atmosphere then acting on all sides
tends to produce equilibrium on the inside and outside of
the mouth as best it may. The communication between
the mouth and pharynx is completely shut off, probably
by the contraction of the pillars of the soft palate and
descent of the latter so as to touch the back of the tongue ;
and the equilibrium, therefore, can be restored only by the
entrance of something through the mouth. The action,
indeed, of the tongue and floor of the mouth in sucking
may be compared to that of the piston in a syringe, and
the muscles which pnll down the os hyoides and tongue,
to the power which draws the handle.

In the preceding account of respiratory actions, the
diaphragm and abdominal muscles have been, as the chief
muscles engaged and for the sake of clearness, almost alone
referred to. But, of course, in all inspiratory actions, the
other muscles of inspiration (p. 195) are also more or less
engaged; and in eapiration, the abdominal muscles are
assisted by others, previously enumerated (p. 199) as
grouped in action with them.

Influence of the Nervous System in Respiration.

Like all other functions of the body, the discharge of
which is necessary to life, respiration must be essentially
an involuntary act. Else, life would be in constant danger,
and would cease on the loss of consciousness for a few
moments, even in sleep. But it is also necessary that
respiration should be to some extent under the control of

Q

226 | RESPIRATION.

the will.. For were it not so, it would be impossible to
perform those voluntary respiratory acts which have been
just enumerated and explained, as speaking, singing,
straining, and the like.

The respiratory movements and their regular rhythm,
so far as they are involuntary and independent of con-
sciousness (as on all ordinary occasions they are), seem to”
be under the absolute governance of the medulla oblon-
gata, which, as a nervous centre, receives the impression
of the “necessity of breathing,” and reflects it to the
phrenic and such other motor nerves as will bring into
co-ordinate and adapted action the muscles necessary to
inspiration. .

In the cases of voluntary respiratory acts, we may
believe that the brain, as well as the medulla oblongata,
is engaged in the process; for we have no evidence of the
mind exercising either perception or will through any
other organ than the brain. But even when the brain
is thus in action, it appears to be the medulla oblongata
which combines the several respiratory muscles to act
together. In such acts, for example as those of cough--
ing and sneezing, the mind first perceives the irritation at
the larynx or nose, and may exercise a certain degree of
. will in determining the actions, as e.g., in the taking of
the deep inspiration which always precedes them. But the
mode in which the acts are performed, and the combi-
nation of muscles to effect them, are determined by the
medulla oblongata, independently of the will, and have
the peculiar character of reflex involuntary movements, in
being always, and without practice or experience, precisely
adapted to the end or purpose.

In these, and in all the other extraordinary respiratory
actions, such as are seen in dyspnoea, or in straining, .
yawning, hiccough, and others, the medulla oblongata
brings into adapted combination of action many other
muscles besides those commonly exerted in respiration.

INFLUENCE OF NERVOUS SYSTEM. 227

Almost all the muscles of the body, in violent efforts of
dyspnoea, coughing, and the like, may be brought into
action at once, or in quick succession; but more particu-
larly the muscles of the larynx, face, scapula, spine, and
abdomen co-operate in these efforts with the muscles of the
chest. These, therefore, are often classed as secondary
muscles of respiration; and the nerves supplying them,
including especially the facial pneumogastric, spinal,
accessory, and external respiratory nerves, were classed
by Sir Charles Bell with the phrenic, as the respiratory
system ofnerves. There appears, however, no propriety in
making a separate system of these nerves, since their mode.
of action is not peculiar, and many besides them co-
operate in the respiratory acts. That which is peculiar
in the nervous influence, directing the extraordinary move-
ments of respiration, is, that so many nerves are com-
bined towards one purpose by the power of a distinct
nervous centre, the medulla oblongata. In other than
respiratory movements, these nerves may act singly or
together, without the medulla oblongata; but after it is
destroyed, no movement adapted to respiration can be per-
formed by any of the muscles, even though the part of the
spinal cord from which they arise be perfect. The phrenic
nerves, for example, are unable to excite respiratory move-
ment of the diaphragm when their connection with the
medulla oblongata is cut off, though their connection with
the spinal cord may be uninjured.* |

Effects of the Suspension and Arrest of Respiration.

These deserve some consideration, because of the illustra-
tion which they afford of the nature of the normal processes
of respiration and circulation. When the process of respi- -
ration is stopped, either by arresting the respiratory move-

* The influence of the nervous system in respiration will be again
and more particularly considered in the section treating of the medulla
oblongata and pneumogastric nerves.

Q 2

228 RESPIRATION,

ments, or permitting them to continue in an atmosphere

deprived of uncombined oxygen, the circulation of blood
through the lungs is retarded, and at length stopped. The
immediate effect of such retarded circulation is an obstruc-
tion to the exit of blood from the right ventricle: this is
followed by delay in the réturn of venous blood to the heart ;
and to this succeeds venous congestion of the nervous centres

and all the other organs of the body. In such retardation, |

also, an unusually small supply of blood is transmitted
through the lungs to the left side of the heart; and this
small quantity is venous.

The condition, then, in which a suffocated, or asphyxi-
ated animal dies is, commonly, that the left side of the
heart is nearly empty, while the lungs, right side of the
heart, and other organs, are gorged with venous blood.
To this condition many things contribute. 1st. The ob-
structed passage of blood through the lungs, which appears
to be the first of the events leading to suffocation, seems
to depend on the cessation of the interchange of gases, as
if blood charged with carbonic acid could not pass freely
through the pulmonary capillaries. But the stagnation of
blood in the pulmonary capillaries would not, perhaps, be
enough to stop entirely the circulation, unless the action
of the heart were also weakened. Therefore, 2ndly, the
fatal result is probably due, in some measure, to the
enfeebled action of the right side of the heart, in conse-
quence of its over-distension by blood continually flowing
into it; this flow, probably, being much increased by the
powerful but fruitless efforts continually made at inspira-
tion (Eccles). And 3rdly, because of the obstruction at the
right side of the heart, there must be venous congestion in
' the medulla oblongata and nervous centres: and this evil
is augmented by the left ventricle receiving and propelling
none but venous blood. Hence, slowness and disorder of the
respiratory movements and of the movements of the heart
may be added. Under all these conditions combined, the

ee ee ——

Ms tates ee ee eee ee |

ud

SUSPENDED ANIMATION. 229

heart at length ceases to act; the cessation of its action
being also in great measure, probably, brought about, 4thly,
by the imperfect supply of oxygenated blood to its muscular
tissue. |

In some experiments performed by a committee ap-
pointed by the Medico-Chirurgical Society to investigate
the subject of Suspended Animation, it was found that, in
the dog, during simple apncea, i.e., simple privation of air,
as by plugging the trachea, the average duration of the
respiratory movements after the animal had been deprived
of air, was 4 minutes 5 seconds; the extremes being
3 minutes 30 seconds, and 4 minutes 40 seconds. The
average duration of the heart’s action, on the other hand,
was 7 minutes II seconds; the extremes being 6 minutes
40 seconds, and 7 minutes 45 seconds. It would seem,
_ therefore, that on an average, the heart’s action continues
for 3 minutes 15 seconds after the animal has ceased to
make respiratory efforts. A very similar relation was ob-
served in the rabbit. Recovery never took place after the
heart’s action had ceased.

The results obtained by the committee on the subject of
drowning were very remarkable, especially in this respect,
that whereas an animal may recover, after simple depriva-
tion of air for nearly four minutes, yet, after submersion in
water for 14 minutes, recovery seems to be impossible.
This remarkable difference was found to be due, not to the
mere submersion, nor directly to the struggles of the
animal, nor to depression of temperature, but to the two
facts, that in drowning, a free passage is allowed to air out
of the lungs, and a free entrance of water into them. In
proof of the correctness of this explanation it was found
that when two dogs of the same size, one, however, having
his windpipe plugged, the other not, were submerged at
the same moment, and taken out after being under water
for 2 minutes, the former recovered on removal of the plug,
the latter did not. It is probably to the entrance of water

230 RESPIRATION.

into the lungs that the speedy death in drowning is mainly
due. The results of post-mortem examination strongly sup-
port this view. On examining the lungs of animals deprived
of air by plugging the trachea, they were found simply
_ congested; but in the animals drowned, not only was the

congestion much more intense, accompanied with ecchy-
mosed points on the surface and in the substance of the
lung, but the air tubes were completely choked up with
a sanious foam, consisting of blood, water, and mucus,
churned up with the air in the lungs by the respiratory
efforts of the animal. The lung-substance, too, appeared
to be saturated and sodden with water, which, stained
slightly with blood, poured out at any point where a section
was made. The lung thus sodden with water was heavy
(though it floated), doughy, pitted on pressure, and was
incapable of collapsing. It is not difficult to understand
how, by such infarction of the tubes, air is debarred
from reaching the pulmonary cells: indeed the inability
of the lungs to collapse on opening the chest is a proof
of the obstruction which the froth occupying the air-tubes
offers to the transit of air. The entire dependence of the
early fatal issue, in apnoea by drowning, upon the open
condition of the windpipe, and its results, was also
strikingly shown by the following experiment. A strong
dog had its windpipe plugged, and was then submerged in
water for four minutes; in three-quarters of a minute after
its release it began to breathe, and in four minutes had fully
recovered. This experiment was repeated with similar results
on other dogs. When the entrance of water into the lungs,
and its drawing up with the air into the bronchial tubes by
means of the respiratory efforts, were diminished, as by
rendering the animal insensible by chloroform previously
to immersion, and thus depriving it of the power of making
violent respiratory efforts, it was found that it could bear
immersion for a longer period without dying than when not
thus rendered insensible. Probably to a like diminution

ANIMAL HEAT. 231

in the respiratory efforts, may also be ascribed the
‘greater length of time persons have been found to bear
submersion’ without being killed, when in a state of in-
toxication, poisoning by narcotics, or during insensibility
from syncope. :

It is to the accumulation of daaNoniie acid in the blood,
and its conveyance into the organs, that we must, in the
first place, ascribe the phenomena of asphyxia. For when
this does not happen, all the other conditions may exist
without injury; as they do, for example, in hybernating
warm-blooded animals. In these, life is supported for
many months in atmospheres in which the same animals,
in their full activity, would be speedily suffocated. During
the periods of complete torpor, their respiration almost
entirely ceases; the heart acts very slowly and feebly; the
processes of organic life are all but suspended, and the
animal may be with impunity completely deprived of atmo-
spheric air for a considerable period. Spallanzani kept a
marmot, in this torpid state, immersed for four hours in
carbonic acid gas, without its suffering any apparent in-
convenienc2. Dr. Marshall Hall kept a lethargic bat under
‘water for 16 minutes, and a lethargic hedgehog for 22}
minutes; and neither of the animals appeared injured by
the experiment.

j a a

CHAPTER VIII.
ANIMAL HEAT.

Tux average temperature of the human body in those
internal parts which are most easily accessible, as the mouth
and rectum, is from 98°5° to 99°5° F.

In different parts of the external surface of the human
body the temperature varies only to the extent of two or
three degrees, when all are alike protected from cooling

‘ /

232 ANIMAL HEAT.

influences; and the difference which under these circum-
stances exists, depends chiefly upon the different degrees of
blood-supply. In the arm-pit—the most convenient situa-
tion, under ordinary circumstances, for examination by the
thermometer—the average temperature is 98°6° F

The chief circumstances by which the temperature of the
healthy body is influenced are the following :—

Aye.—The average temperature of the new-born child 4 is
only about 1° F. above that proper to the adult; and the
difference becomes still more trifling during infancy and
early childhood. According to Wunderlich, the temperature
falls to the extent of about +° to 3° F. from early infancy
to puberty, and by about the same amount from puberty to
fifty or sixty years of age. In old age the temperature
again rises, and approaches that of infancy.

Although the average temperature of the body, however,
is not lower than that of younger persons, yet the power of
resisting cold is less in them—exposure to a low temperature
causing a greater reduction of heat than in young persons.

The same rapid diminution of temperature was observed

by M. Edwards in the new-born young of most carnivorous. ©

and rodent animals when they were removed from the
parent, the temperature of the atmosphere being between
50° and 533° F.; whereas, while lying close to the body of
the mother, their temperature was only 2 or 3 degrees
lower than hers. The same law applies to the young of
birds. Young sparrows, a week after they were hatched,
had a temperature of 95° to 97°, while in the nest; but
when taken from it, their temperature fell in one hour to
664°, the temperature of the atmosphere being at the time
624°. It appears from his investigations, that in respect
of the power of generating heat, some Mammalia are born
in a less developed condition than others; and that the
young of dogs, cats, and rabbits, for example, are inferior
to the young of those animals which are not born blind.
The need of external warmth to keep up the temperature

=.

TEMPERATURE OF THE BODY. ies:

of new-born children is well known; the researches of M.
Edwards show, that the want of it is, as Hunter suggested,
a much more frequent cause of death in new-born children
than is generally supposed, and furnish a strong argument
against the idea, that children, by early exposure to cold,
can soon be hardened into resisting its injurious influence.

Sex.—The average temperature of the female would
appear from observations by Dr. Ogle to be very slightly
higher than that of the male.

Period of the Day. The temperature undergoes a gradual
alteration, to the extent of about 1- to 13° F. in the course
of the ‘day and night; the minimum being at night or in
the early morning, the maximum late in the afternoon.

Exercise.—Active exercise raises the temperature of the
body. This may be partly ascribed to the fact, that every
muscular contraction is attended by the development of one
or two degrees of heat in the acting muscle; and that the
heat is increased according to the number and rapidity of
these contractions, and is quickly diffused by the blood
circulating from the heated muscles. Possibly, also, some
heat may be generated in the various movements, stretch-
ings, and recoilings of the other tissues, as the arteries,
whose elastic walls, alternately dilated and contracted, may
give out some heat, just as caoutchouc alternately stretched
and recoiling becomes hot. “But the heat thus developed
cannot be great.

Moreover, the increase of temperature throughout the
whole body, produced by active exercise, is but small; the
great apparent increase of heat depending, in a great
measure, on the increased circulation and quantity of blood,
and, therefore, greater heat, in parts of the body (as the
skin, and especially the skin of the extremities), which, at
the same time that they feel more acutely than others any
changes of temperature are, under ordinary conditions, by
some degrees colder than organs more centrally situated.

That the increased temperature of the skin during

234 ANIMAL HEAT.

exercise is not accompanied by a proportional increase of
the heat of other parts, which are naturally much warmer,
is well shown by some observations of Dr. J. Davy.

Climate and Season.—In passing from a temperate to a
hot climate the temperature of the human body rises
slightly, the increase rarely exceeding 2° to 3° F. In
summer the temperature of the body is a little higher than
in winter; the difference amounting to from 1° to 4° F.
( Wunderlich).

The same effects are observable in alterations of tem-
_ perature not depending on season or climate.

Food and Drink.—The effect of a meal upon the tempera-
ture of a body is but small. A very slight rise usually occurs.

Cold alcoholic drinks depress the temperature somewhat
(3° to 1° F.). Warm alcoholic drinks, as well as warm tea
and coffee, raise the temperature (about }° F.).

In disease the temperature of the ‘body deviates from the
normal standard to a greater extent than would be antici-
pated from the slight effect of external conditions during
health. Thus, in some diseases, as pneumonia arid typhus,
it occasionally rises as high as 106° or 107° F.; and con-
siderably higher temperatures have been noted. In a case
of malignant fever recently recorded by Mr. Norman Moore,
the temperature in the axilla rapidly rose to 111° F.; when
the patient died. The highest> temperature recorded in a
living man, 112°5° F., was observed by Wunderlich, in a
cease of idiopathic tetanus, at the time of death. In the
morbus c@ruleus, in which there is defective arterialization
of the blood from malformation of the heart, the tem-
perature of the body may be as low as 79° or 774°; in
Asiatic cholera a thermometer placed in the mouth some-
time rises only to 77°or 79°; and in a case of tubercular
meningitis, observed by Dr. Gee, the temperature of the
rectum remained for hours at 79°4° F.

The temperature maintained by Mammalia in an active

state of life, according to the tables of Tiedemann and
/

. FOOD AND DRINK. 235

Rudolphi, averages 101°. The extremes recorded by them
were 96° and 106”, the former in the narwhal, the latter in
a bat (Vespertilio Pipistrella). In birds, the average is as
high as 107°; the highest temperature, 111°25°, being in
the small eda the linnets, etc. Among reptiles, Dr.
John Davy found, that while the medium they were in was
75°, their average temperature was 82°5°. As a general
rule, their temperature, though it falls with that of the
surrounding medium, is, in temperate media, two ‘or
more degrees higher ; and though it rises also with that of
the medium, yet at very high degrees it ceases to do so,
and remains even lower than that of the medium. Fish
and Invertebrata present, as a general rule, the same tem-
perature as the medium in which they live, whether that
be high or low; only among fish, the tunny tribe, with
strong hearts and red meat-like muscles, and more blood
than the average of fish have, are generally 7° warmer
than the water around them.

-' The difference, therefore, between what ‘are commonly
called the warm- and the cold-blooded animals, is not one
of absolutely Ligher or lower temperature ; for the animals
which to us, in a temperate climate, feel cold (being like
the air or water, colder than the surface of our bodies),
would, in an external temperature of 100°, have nearly the
same temperature and feel hot tous. The real difference
is, as Mr. Hunter expressed it, that what we call warm-
blooded animals (birds and Mammalia), have a certain
*‘permanent heat in all atmospheres,” while the tempera-
ture of the others, which we call cold-blooded, is ‘‘ variable
with every atmosphere.”

The power of maintaining a uniform temperature, which
Mammalia and birds possess, is combined with the want of
power to endure such changes of temperature of their bodies
as are harmless to the other classes; and when their power
of resisting change of temperature ceases, they suffer serious
disturbances or die.

236 ANIMAL HEAT.

Sources and Mode of Production of Heat in the Body.

In explaining the chemical changes effected in the pro-
cess of respiration (p. 219), it was stated that the oxygen
of the atmosphere taken into the blood is combined, in the
course of the circulation, with the carbon and the hydrogen
of disintegrated and absorbed tissues, and of certain ele-
ments of food which have not been converted into tissues.
That such a combination between the oxygen of the atmo-
sphere and the carbon and hydrogen in the blood, is coa-
tinually taking place, is made certain by the fact, that a
larger amount of carbon and hydrogen is constantly being
added to the blood from the food than is required for the
ordinary purposes of nutrition, and that a quantity of
oxygen is also constantly being absorbed from the air in
the lungs, of the disposal of which no account can be given
except by regarding it as combining, for the most part,
with the excess of carbon and hydrogen, and being excreted
in the form of carbonic acid and water. In other words,
the blood of warm-blooded animals appears to be always
receiving from the digestive canal and the lungs more
carbon, hydrogen, and oxygen than are consumed in the
repair of the tissues, and to be always emitting carbonic
acid and water, for which there is no other known source
than the combination of these elements.* By such com-
bination, heat is continually produced in the animal body.
The same amount of heat will be evolved in the union of ©
any given quantities of carbon and oxygen, and of hydrogen
and oxygen, whether the combination be rapid and evident,
as in ordinary combustion, or slow and imperceptible, as in
the changes which occur in the living body. And since
the heat thus arising will be generated wherever the blood

* Some heat will also be generated in the combination of sulphur and
phosphorus with oxygen, to which reference has been made (p. 216) ;
but the amount thus produced is but small.

ep te

PRODUCTION OF HEAT. 237

is carried, every part of the body will be heated equally, or
nearly so.

This theory, that the maintenance of the temperature of |
theliving body depends on continual chemical change, chiefly

_ by oxidation, of combustible materials existing in the tissues
_ and in the blood, has long been established by the demon-

stration that the quantity of carbon and hydrogen which,

| in a given time, unites in the body with oxygen, is suffi-

cient to account for the amount of heat generated in the |
animal within the same time: an amount capable of main-
taining the temperature of the body at from 98° to 100°, |
notwithstanding a large loss by radiation and evaporation. |

Many things observed in the economy and habits of
animals are explicable by this theory, and may here briefly
be quoted, although no longer required as additional
evidence for its truth. Thus, as a general rule, in the
various classes of animals, as well as in individual ex-
amples of each class, the quantity of heat generated in
the body is in direct proportion to the activity of the
respiratory process. ‘The highest animal. temperature, for)
example, is found in birds, in whom the function of
respiration is most actively performed. In Mammalia, the
process of. respiration is less active, and the average tem
perature of the body less, than in birds. In reptiles, both
the respiration and the heat are at a much lower standard ;
while in animals below them, in which the function of
respiration is at the lowest point, a power of producing
heat is, in ordinary circumstances, hardly discernible.
Among these lower animals, however, the observations of
Mr. Newport supply confirmatory evidence. He shows
that the larva, in which the respiratory organs are smaller
in comparison with the size of the body, kas a lower tem-
perature than the perfect insect. Volant insects have the
highest temperature, and they have always the largest
respiratory organs and breathe the greatest quantity of air ;
while among terrestrial insects, those also produce the most

238 ANIMAL HEAT.

heat which have the largest respiratory organs and breathe
the most air. During sleep, hybernation, and other states
of inaction, respiration is slower or suspended, and the
temperature is proportionately diminished ; while, on the
other hand, when the insect is most active and respiring
most voluminously, its amount of temperature is at its
maximum, and corresponds with the quantity of -respi-
ration. Neither the rapidity of the circulation, nor the
size of the nervous system, according to Mr. Newport,
presents such a constant relation to the evolution of heat.

On the Regulation of the Temperature of the Human Body.

The continual: production of heat in the body has been
already referred to. There is also, of necessity, a continual
loss. But in healthy warm-blooded animals, as already
remarked, the loss and gain of heat are so nearly balanced
one by the other, that under all ordinary circumstances,
an uniform temperature, within two or three degrees, is
preserved.

The loss of heat from the human body takes plans chiefly
by radiation and conduction from its surface, and by means.
of the constant evaporation of water from the same part,
and from the air-passages. In each act of respiration,
heat is also lost by so much warmth as the expired air
acquires (p. 210). All food and drink which enter the
body at a lower temperature than itself, abstract a small
measure of heat, and the urine and freces take about a like
amount away, when they leave the body. Lastly, some
part of the heat of the body is-rendered imperceptible, and
therefore lost as heat, by being manifested in the form of
mechanical motion.

By far the most important loss of heat from the body,—
probably 80 or go per cent. of the whole amount, is that
which proceeds from radiation, conduction, and evapora-
tion from the skin. And it is to this part especially, and
in a smaller measure to the air-passages, that we must look

REGULATION OF THE TEMPERATURE. 239

for the means by which the temperature is regulated; in
other words, by which it is prevented from rising beyond
the normal point on the one hand, or sinking below it on
the other. The chief indirect means for accomplishing the
~ game end are, variations in the amount and quality of the
food and drink taken, variations in clothing, and in
exposure to external heat or cold.

In order to understand the means by which the heat of
the body is regulated, it is necessary to take into consi-
deration the following facts: First, the immediate source
of heat in the body is the presence of a large quantity of
a warm fluid—the blood, the temperature of which is, in
health, about 100° F. In the second place, the blood,
while constantly moving in a multitude of different streams,
is, every minute or so, gathered up in the heart into one
large stream, before being again dispersed to all parts of
the body. In this way, the temperature of the blood.
remains almost exactly the same in all parts; for while a
portion of it in passing through one organ, as the skin,
may become cooler, and through another organ, as the
liver, may become warmer, the effect on each separate
stream is more or less neutralized when it mingles with
another, and an average is struck, so to speak, for all the
streams when they form one, in passing through the
heart..

The means by which the skin is able to act as one of
the most important organs for regulating the temperature
of the blood, are—(1), that it offers a large surface for
radiation, conduction, and evaporation; (2), that it con-
tains a large amount of blood; (3), that the quantity of
blood contained in it is the greater under those circum-
stances which demand a loss of heat from the body, and
vice versd. For the circumstance which directly determines.
the quantity of blood in the skin, is that which governs
the supply of blood to all the tissues and organs of the
body, namely, the power of the vaso-motor nerves to cause

240 ANIMAL HEAT.

a greater or less tension of the muscular element in the
walls of the arteries (see p. 141), and, in correspondence
with this, a lessening or increase of the calibre of the vessel
accompanied by a less or greater current of blood. A
warm or hot atmosphere so acts on the nerve fibres of the
skin, as to lead them to cause in turn a relaxation of the
muscular fibre of the blood-vessels; and, as a result, the
skin becomes full-blooded, hot, and sweating; and much
heat is lost. With a low temperature, on the other hand,
the blood-vessels shrink, and in accordance with the con-
sequently diminished blood-supply, the skin becomes pale,
and cold, and dry. Thus, by means of a self-regulating
apparatus, the skin becomes the most important of the
means by which the temperature of the body is regulated.

| In connection with loss of heat by the skin, reference
has been made to that which occurs both by radiation
and conduction, and by evaporation; and the subject of
animal heat has been considered almost solely with regard
to the ordinary case of man living in a medium colder than
his body, and therefore losing heat in all the ways men-
tioned. The importance of the means, however, adopted,

so to speak, by the skin for regulating the temperature of -

the body, will depend on the conditions by which it is sur-
rounded; an inverse proportion existing in most cases
between the loss by radiation and conduction on the one
hand, and by evaporation on the other. Indeed, the small
loss of heat by evaporation in cold climates may go far to
compensate for the greater loss by radiation; as, on the
other hand, the great amount of fluid evaporated in hot
air may remove nearly as much heat as is commonly lost
by both radiation and evaporation in ordinary tempera-
tures; and thus, it is possible, that the quantities of heat
required for the maintenance of an uniform proper tem-
perature in various climates and seasons are not so different
as they, at first thought, seem.

Many examples might be given of the power which the

.
= eee Fe) ee ee ee

REGULATION OF HEAT: 241

body possesses of resisting the effects of a high tempera-
ture, in virtue of evaporation from the skin.

Sir Charles Blagden and others supported a temperature
varying between 198° and 211° F. in dry air for several
minutes; and in a subsequent experiment he remained
eight minutes in a temperature of 260°. But such heats
are not tolerable when the air is moist as well as hot, so
as to prevent evaporation from the body. Mr. C. James
states, that in the vapour baths of Nero he was almost
suffocated in a temperature of 112°, while in the caves of
Testaccio, in which the air is dry, he was but little incom-
moded by a temperature of 176°. In the former, evapo-
ration from the skin was impossible; in the latter, it was,
probably, abundant, and the layer of vapour which would
rise from all the surface of the body would, by its very
slowly conducting power, defend it for a time from the full
action of the external heat.

_ (The glandular apparatus, by which secretion of fluid
from the skin is effected, will be considered in the Section
on the Skin.)

The ways.by which the skin may be rendered more
efficient as a cooling-apparatus by exposure, by baths, and
by other means, which man instinctively adopts for lower-
ing his temperature when necessary, are too well known to
need more than to be mentioned.

As a means for lowering the temperature, the lungs and
air-passages are very inferior to the skin; although, by
giving heat to the air we breathe, they stand next to the
skin in importance. As a regulating power, the inferiority
is still more marked. The air which is expelled from
the lungs leaves the body at about the temperature of
the blood, and is always saturated with moisture. No
inverse proportion, therefore, exists between the loss of
heat by radiation and conduction on the one hand, and
by evaporation on the other. The colder the air, for
example, the greater will be the loss in all ways. Neither

R

242 ANIMAL HEAT.

is the quantity of blood which is exposed to the cooling
influence of the air diminished or increased, so far as is
known, in accordance with any need in relation to tempe-
rature. It is true that by varying the number and depth
of the respirations, the quantity of heat given off by the
- lungs may be made, to some extent, to vary also. But the
respiratory passages, while they must be considered important
means by which heat is lost, are altogether subordinate in
the power of regulating the temperature, to the skin.

It may seem to have been assumed, in the foregoing
pages, that the only regulating apparatus for temperature
required by the human body is one that shall, more or less,
produce a cooling effect; and as if the amount of heat pro-
duced were always, therefore, in excess of that which is
required. Such an assumption would be incorrect. We
have the power of regulating the production of heat, as
well as its loss.

In food we have a means for elevating our temperature.
It is the fuel, indeed, on which animal heat ultimately
depends altogether. Thus, when more heat is wanted, we
instinctively take more food, and take such kinds of it as
are good for combustion ; while everyday experience shows
the different power of resisting cold possessed by the well-
fed and by the starved.

In northern regions, again, and in the colder seasons of
more southern climes, the quantity of food consumed is
(speaking very generally) greater than that consumed by
the same men or animals in opposite conditions of climate
and seasons. And the food which appears naturally
adapted to the inhabitants of the coldest climates, such as
the several fatty and oily substances, abounds in carbon
and hydrogen, and is fitted to combine with the large
quantities of oxygen which, breathing cold dense air, they
absorb from their lungs.

In exercise, again, we have an important means of
raising the temperature of our bodies (p. 233).

’ a. hh te,

a fe ~~. lee ee

INFLUENCE OF NERVOUS SYSTEM. 243

The influence of externa! coverings for the body must not
be unnoticed. In warm-blooded animals, they are always
adapted, among other purposes, to the maintenance of
uniform temperature ; and man adapts for himself such as
are, for the same purpose, fitted to the various climates to
which he is exposed. By their means, and by his command
over food and fire, he maintains his temperature on all
accessible parts of the surface of the earth.

The influence of the nervous system in modifying the pro-
duction of heat has been already referred to. The experi-
ments and observations which best illustrate it are those
showing, first, that when the supply of nervous influence
to a part is cut off, the temperature of that part falls below
its ordinary degree; and, secondly, that when death is
caused by severe injury to, or removal of, the nervous
centres, the temperature of the body rapidly falls, even
though artificial respiration be performed, the circulation
Maintained, and to all appearance the ordinary chemical
changes of the body be completely effected. It has been
repeatedly noticed, that after division of the nerves of a
limb, its temperature falls; and this diminution of heat
has been remarked still more plainly in limbs deprived of
nervous influence by paralysis. For example, Mr. Earle
found the temperature of the hand of a paralysed arm to
be 70°, while the hand of the sound side had a tempera-
ture of 92° F. On electrifying the paralysed limb, the
temperature rose to 77°. In another case, the temperature
of the paralysed finger was 56° F., while that of the un-
affected hand was 62°.

With equal certainty, though less definitely, the influence
of the nervous system on the production of heat, is shown
in the rapid and momentary increase of temperature,
sometimes general, at other times quite local, which is
observed in states of nervous excitement; in the general
increase of warmth of the body, sometimes amounting to

perspiration, which is excited by passions of the mind; in
R 2

244 | ANIMAL HEAT.

the sudden rush of heat to the face, which is not a mere
sensation; atid in the equally rapid diminution of tem-
perature in the depressing passions. But none of these
instances suffices to prove that heat is generated by mere
nervous action, independent of any chemical change; all
are explicable, on the supposition that the nervous system
alters, by its power of controlling the caiibre of the blood-
vessels (p. 141), the quantity of blood supplied to a part;
while any influence which the nervous system may have in
the production of heat apart from this influence on the
blood-vessels, is an indirect one, and is derived from
its power of causing nutritive change in the tissues, which
may, by involving the necessity of chemical action, involve
the production of heat. The existence of nerves, which
regulate animal heat otherwise than by their influence
in trophic (nutritive) or vaso-motor changes, although by
many considered probable, is not yet proven.

In connection with the regulation of animal tempera-
ture, and its maintenance in health at the normal height,
it is interesting to note the result of circumstances too
powerful, either in raising or lowering the heat of the body,
to be controlled by the proper regulating apparatus.
Walther found that rabbits and dogs, when tied to a board
and exposed to a hot sun, reached a temperature of
114'8° F., and then died. Cases of sunstroke furnish us
with similar examples in the case of man; for it would
seem that here death ensues chiefly or solely from elevation
of the temperature. In a case related by Dr. Gee, the
temperature in the axilla was 109°5° F.: and in many
febrile diseases the immediate cause of death appears to be
the elevation of the temperature to a point inconsistent
with the continuance of life.

The effect of mere loss of bodily temperature in man is —
less well known than the effect of heat.

From experiments by Walther, it appears that rabbits
can be cooled down to 48° F. before they die, if artificial

FOOD. 245

respiration be kept up. Cooled down to 64° F., they can-
not recover unless external warmth be applied together
with the employment of artificial respiration. Rabbits
not cooled below 77° F. recover by external warmth
alone.

CHAPTER IX.
DIGESTION.

DicxEstion is the process by which those parts of our
food which may be employed in the formation and repair
of the tissues, or in the production of heat, are made fit to
be absorbed and added to the blood.

Food.

Food may be considered in its relation to these two pur-
poses—the nutrition of the tissues, and the production of
heat. But, under the first of these heads will be included
many other allied functions, as, for example, secretion and
generation :.and under the second, not the production of
heat only as such, but of all the other forces correlated
with it, which are manifested by the living body.

The following is a convenient tabular classification of
the usual and more necessary kinds of food :—

NITROGENOUS :— |

Proteids, as Albumen, Casein, Syntonin, Gluten, and their allies,
and Gelatin ; (containing Carbon, Hydrogen, Oxygen, and Nitrogen ;
some of them, also Sulphur and Phosphorus).

Non-NitrRoGENnous :—

(1). Amyloids—Starch, Sugar, and their allies Se apsesie Carbon,
Hydrogen and Oxygen).

(2). Oils and Fats (containing Carbon, Hydrogen, and Oxygen; the
oxygen in much smaller proportion than in starch or sugar).

(3). Mineral or Saline Matters ; as Chloride of Sodium, Phosphate of
Lime, ete.

(4). Water.

246 DIGESTION.

Animals cannot subsist on any but organic substances,
and these must contain the several elements and com-
pounds which are naturally combined with them: in other
words, not even organic compounds are nutritive unless,
they are supplied in their natural state. Pure fibrin, pure
gelatin, and other principles purified from the substances
naturally mingled with them, are incapable of supporting
life for more than a brief time.

Moreover, health cannot be maintained by any number
of substances derived exclusively from one only of the two
chief groups of alimentary principles mentioned above. A
mixture of nitrogenous and non-nitrogenous organic sub-
stances, together with the inorganic principles which are
severally contained in them, is essential to the well-being
and, generally, even to the existence of an animal. The
truth of this is demonstrated by experiments performed for
the purpose, and is illustrated by the composition of the
food prepared by nature as the exclusive source of nou-
rishment to the young of Mammalia, namely, milk.

COMPOSITION OF MILK.

Human. Cows.

Water . ; : SO! ; : . 858
Solids. - « % *SEO : ; Pers
1,000 1,000

Casein . ; ; ae: Se ‘ . - 68
Butter. ; cick ae p ; Se
Sugar (with extractives) 48 . : ; - 30
Salts P ° exe 2 . . oe 0% 6
110 142

In milk, as will be seen from the preceding table, the
albuminous group of aliments is represented by the casein,
the oleaginous by the butter, the aqueous by the water,
the saccharine by the sugar of milk. Among the salts of
milk are likewise phosphate of lime, alkaline, and other
salts, and a trace of iron; so that it may be briefly said

COMPOSITION OF EGGS. 247

to include all the substances which the tissues of the
growing animal need for their nutrition, and which are
required for the production of animal heat.

The yelk and albumen of eggs are in the same relation
as food for the embryoes of oviparous animals, that milk is
to the young of Mammalia, and afford another example of
mixed food being provided as the most perfect nutrition.

CoMPposITION oF Fowts’ Eaas.
White. Yelk.

_ Water : ; . 800 : 3 es
Albumen ‘ Fe SRE fs ‘ idripvaj
Mucus } , . 4°5 Yellow Oil . 28°75
Salts . ‘ “aves” xt ; © tte

Experiments illustrating the same principle have been
performed by Magendie and others. Dogs were fed ex-
clusively on sugar and distilled water. During the first
seven or eight days they were brisk and active, and took
their food and drink as usual; but in the course of the
second week, they began to get thin, although their appe-
tite continued good, and they took daily between six and
eight ounces of sugar. The emaciation increased during
the third week, and they became feeble, and lost their
activity and appetite. Atthe same time an ulcer formed
on each cornea, followed by an escape of the humours of
the eye: this took place in repeated experiments. The
animals still continued to eat three or four ounces of sugar
daily ; but became at length so feeble as to be incapable of
motion, and died on a day varying from the thirty-first to
the thirty-fourth. On dissection, their bodies presented all
the appearances produced by death from starvation; in-
deed, dogs will live almost the same length of time without
any food at all.

When dogs were fed exclusively on gum, results almost
similar to the above ensued. When they were kept on
olive-oil and water, all the phenomena produced were the
same, except that no ulceration of the cornea took place:

248 DIGESTION.

the effects were also the same with butter. Tiedemann
and Gmelin obtained very similar results. They fed
different geese, one with sugar and water, another with
gum and water, and a third with starch and water. All
gradually lost weight. The one fed with gum died on the
sixteenth day ; that fed with sugar, on the twenty-second ;
the third, which was fed with starch, on the twenty-fourth ;
and another on the twenty-seventh day; having lost,
during these periods, from one-sixth to one-half of their
weight. The experiments of Chossat and Letellier prove
the same; and in men, the same is shown by the various
diseases to which they who consume but little nitrogenous
food are liable, and especially, as Dr. Budd has shown,
by the affection of the cornea which is observed in Hindus
feeding almost exclusively on rice. But it is not only the
non-nitrogenous substances, which, taken alone, are in-
sufficient for the maintenance of health. The experiments
of the Academies of France and Amsterdam were equally
conclusive that gelatin alone soon ceases to be nu-
tritive. ai |
Mr. Savory’s observations on food confirm and extend
the results obtained by Magendie, Chossat, and others.
They show that animals fed exclusively on non-nitrogenous
diet speedily emaciate and die, as if from starvation; that
a much larger amount of urine is voided by those fed with
nitrogenous than by those with non-nitrogenous food; and
that animal heat is maintained as well by the former as
by the latter—a fact which proves that nitrogenous elements
of food, as well as non-nitrogenous may be regarded as
calorifacient. ,The non-nitrogenous principles, however,
he believes to be calorifacient essentially, not being first
converted into tissue; but of the nitrogenous, he believes
that only a part is thus directly calorifacient, the rest
being employed in the formation of tissue. Contrary to
the views of Liebig and Lehmann, Savory has shown that,
while animals speedily die when confined to non-nitro-

=a * —. »

EXPERIMENTS WITH DIFFERENT FOODS. 249

_ genous diet, they may live long when fed exclusively with
nitrogenous food.

Man is supported as well by food constituted wholly of
animal substances, as by that which is formed entirely of
vegetable matters, on the condition, of course, that it
contain a mixture of the various nitrogenous and non
nitrogenous substances just shown to be essential for
healthy nutrition. In the case of carnivorous animals, the
food upon which they exist, consisting as it does of the
flesh and blood of other animals, not only contains all the
elements of which their own blood and tissues are com-
posed, but contains them combined, probably in the same
forms. Therefore little more may seem requisite, in the
preparation of this kind of food for the nutrition of the
body, than that it should be dissolved and conveyed into
the blood in .a condition capable of being re-organized.
- But in the case of the herbivorous animals, which feed ex-
clusively upon vegetable substances, it might seem as if.
there would be greater difficulty in procuring food capable
of assimilation into their blood and tissues. But the chief
ordinary articles of vegetable food contain substances
identical in composition, with the albumen, fibrin, and
casein, which constitute the principal nutritive materials in
animal food. Albumen is abundant in the juices and
seeds of nearly all vegetables; the gluten which exists,
especially in corn and other seeds of grasses as well as in
their juices, is identical in composition with fibrin, and is
often named vegetable fibrin; and the substance named
legumen, which is obtained especially from peas, beans,
and other seeds of leguminous plants, and from the potato,
is identical with the casein of milk. All these vegetable
substances are, equally with the corresponding animal
principles, and in the same manner, capable of conversion
into blood and tissue; and as the blood and tissues in both
classes of animals are alike, so also the nitrogenous food of
both may be regarded as, in essential respects, similar.

250 . DIGESTION.

It is in the relative quantities of the nitrogenous and
non-nitrogenous compounds in these different foods that
the difference lies, rather than in the presence of substances
in one of them which do not exist in the other. The only
non-nitrogenous compounds in ordinary animal food are
the fat, the saline matters, and water, and, in some in-
stances, the vegetable matters which may chance to be in
the digestive canals of such animals as are eaten whole.
The amount of these, however, is altogether much less
than that of the non-nitrogenous substances represented by
the starch, sugar, gum, oil, etc., in the vegetable food of
herbivorous animals.

The effects of total deprivation of food have been made
the subject of experiments on the lower animals, and have
been but too frequently illustrated in man.

(1). One of the most notable effects of starvation, as
might be expected, is loss of weight; the loss being greatest
at first, as a rule, but afterwards not varying very much,
day by day, until death ensues. Chossat found that the
ultimate proportional loss was, in different animals experi-
mented on, almost exactly the same; death occurring
when the body had lost two-fifths (forty per cent.) of its
original weight.

Different parts of the body lose weight in very different
proportions. The following results are taken, in round
numbers, from the table given by M. Chossat :-—

Fat loses. , P . - 93 per cent.
Blood . ‘ " - Supe cree os
Spleen ; P ‘: . ae “3
Pancreas ; : $ ‘as Oe ;
Liver. é < . : 2358 *%
Heart . ° ° « « yo 5 44 R
Intestines . - ° ° « 42 ms
Muscles of locomotion . $5 aoa “m

Stomach loses . ° e « 39 ”

~

STARVATION. 251

Pharynx, eee » + 34 per cent.

Skin . -. ° s 933 x

Kidneys. . ‘ Mt fate} ee

Respiratory apoepeeus : : - a

Bones . - : ° tre Fe

Eyes . . . : ° . Io 9

Nervous system. dw. he s UF >» (nearly).

(2). The effect of starvation on the temperature of the
various animals experimented on by Chossat was very
marked. For some time the variation in the daily tempe-
rature was more marked than its absolute and continuous
dimunition, the daily fluctuation amounting to 5° or 6° F.,
instead of 1° or 2° F., as in health. But a short time
before death, the temperature fell very rapidly, and death
ensued when the loss had amounted to about 30° F. It has |
been often said, and with truth, although the statement
requires some qualification, that death by starvation is

‘really death by cold; for not only has it been found that

differences of time with regard to the period of the fatal
result are attended by the same ultimate loss of heat, but
the effect of the application of external warmth to animals
cold and dying from starvation, is more effectual in reviving
them than the administration of food. In other words, an
animal exhausted by deprivation of nourishment is unable
so to digest food as to use it as fuel, and therefore is de-
pendent for heat on its supply from without. Similar
facts are often observed in the treatment of exhaustive
diseases in man.

(3). The symptoms produced by starvation in the human
subject are hunger, accompanied, or it may be replaced, —
by pain, referred to the region of the stomach; insatiable
thirst; sleeplessness; general weakness and emaciation.
The exhalations both from the lungs and skin are footid,
indicating the tendency to decomposition which belongs
to badly-nourished tissues; and death occurs, sometimes
after the additional exhaustion caused by diarrhcea, often

2haee DIGESTION.

with symptoms of nervous. disorder, delirium, or con-
vulsions. r

(4). In the human subject death commonly occurs
within six to ten days after total deprivation of food. But
this period may be considerably prolonged by taking a
very small quantity of food, or even water only. The
cases so frequently related of survival after many days, or
even some weeks, of abstinence, have been due either to
the last-mentioned circumstances, or to others less effectual,
which prevented the loss of heat and moisture. Cases in
which life has continued after total abstinence from food
and drink for many weeks, or months, exist only in the
imagination of the vulgar.

(5). The appearances presented after death from starva-
tion are those of. general wasting and bloodlessness, the
latter condition being least noticeable in the brain. The
stomach and intestines are empty and contracted, and the
walls of the latter usually appear remarkably thinned and
almost transparent. The usual secretions are scanty or
absent, with the exception of the bile, which, somewhat
concentrated, usually fills the gall-bladder. All parts of
the body readily decompose.

It has just been remarked that man can live upon
animal matters alone, or upon vegetables. The structure
of his teeth, however, as well as experience, seems
to declare that he is best fitted for a mixed diet; and
the same inference may be readily gathered from other
facts and considerations. Thus, the food a man takes
into his body daily, represents or ought to represent the
quantity and kind of matter necessary for replacing that
which is daily cast out by the way of lungs, skin, kidneys,
and other organs. To find out, therefore, the quantity
and kind of food necessary for a healthy man, it will,
evidently, be the best plan to consider in the first place
what he loses by excretion.

2

Gs

DAILY LOSS OF CARBON AND NITROGEN. 253

For the sake of example, we may now take only two
elements, carbon and nitrogen, and, if we discover what
amount of these is respectively discharged in a given time
from the body, we shall be in a position to judge what
kind of food will most readily and economically replace
their loss.

The quantity of carbon daily lost from the body amounts
to about 4,500 grains, and of nitrogen 300 grains; and
if a man could be fed by these elements, as such, the
problem would be a very simple one; a corresponding
weight of charcoal, and, allowing for the oxygen in it,

of atmospheric air, would be all that is necessary. But,

as before remarked, an animal can live only upon these
elements when they are arranged in a particular man-
ner with others, in the form of an organic compound, as
albumen, starch, and the like; and the relative propor-
tion of carbon to nitrogen in either of these compounds

_alone, is, by no means, the proportion required in the

diet of man. The amount, 4,500 grains of carbon, repre-
sents about fifteen times the quantity of nitrogen required
in the same period; and, in albumen, the proportion of
carbon to nitrogen is only as 3°5 to 1. If, therefore, a man
took into his body, as food, sufficient albumen to supply
him with the needful amount of carbon, he would receive
more than four times as much nitrogen as he wanted ;
and if he took only sufficient to supply him with nitrogen,
he would be starved for want of carbon. It is plain,
therefore, that he should take with the albuminous part
of his food, which contains so large a relative amount
of nitrogen in proportion to the carbon he needs, sub-
stances in which the nitrogen exists in much smaller
quantities.

Food of this kind is provided in such compounds as
starch and fat. The latter indeed as it exists for the most
part in considerable amount mingled with the flesh of

animals, removes to a great extent, in a diet of animal *

Lk” Ayn
y WY

254 . DIGESTION.

food, the difficulty which would otherwise arise from a
deficiency of carbon—fat containing a large relative pro-
portion of this element, and no nitrogen.

To take another example; the proportion of carbon to
nitrogen in bread is about 30 to 1. If a man’s diet were
confined to bread, he would eat, therefore, in order to
obtain the requisite quantity of nitrogen, twice as much
carbon as is necessary; and it is evident, that, in this
instance, a certain quantity of a substance with a large
relative amount of nitrogen is the kind of food necessary
for redressing the balance.

To place the preceding facts in a tabular form, and
taking meat as an example instead of pure albumen :—
meat contains about 10 per cent. of carbon, and rather
more than 3 per cent. of nitrogen. Supposing a man to
take meat for the supply of the needful carbon, he would
require 45,000 grains, or nearly 6} lbs., containing :—

Carbon . ° ° ° , = , - 4,500 grains
Nitrogen . ; : hs a ie
Excess of Nitrogen ies the salle required 1,500 ,,

Bread contains about 30 per cent. of carbon and I. per
cent. of nitrogen.

If bread alone, therefore, were taken as food, a man
would require, in order to obtain the requisite nitrogen,
30,000 grains, containing—

Carbon . . 3 . . . > + 9,000 grains

Nitrogen . ; Pre ee
Excess of Carbon itiows e the titer Kent ed =. 4500-5,

But a combination of bread and meat would supply
much more economically what was necessary. Thus—

Carbon. Nitrogen.
15,000 grains of bread (or rather more than
2 lbs.) contain ‘ : . 4,500grs. 150 grs
5,000 grains of meat (or about 3 Ib. ) oat 500 ,, I50 ,,

5,000 ,, 300 +»,

NECESSITY FOR CHANGES OF DIET. 255

So that 3 1b. of meat, and less than 2 lbs. of bread,
would supply all the needful carbon and nitrogen with but
little waste.

From these facts it will be plain that a mixed diet is the
best and most economical food for man; and the result of
experience entirely coincides with what might have been
anticipated on theoretical grounds only.

It must not be forgotten, however, that the value of
certain foods may depend quite as much on their digesti-
bility, as on the relative quantities of the necessary
elements which they contain.

In actual practice, moreover, the quantity and kind of
food to be taken with most economy and advantage cannot
be settled for each individual, only by considerations of the
exact quantities of certain elements that are required.
Much will! of necessity depend on the habits and digestive
powers of the individual, on the state of his excretory

organs, and on many other circumstances. Food which to

one person is appropriate enough, may be quite unfit for
another; and the changes of diet so instinctively prac-
tised by all to whom they are possible, have much more
reliable grounds of justification than any which could be
framed on theoretical considerations only.

In many of the experiments on the digestibility of
various articles of food, disgust at the sameness of the
diet may have had as much to do with inability to consume
and digest it, as the want of nutritious properties in the
substances which were experimented on. And that disease
may occur from the want of particular food, is well shown
by the occurrence of scurvy when fresh vegetables are
deficient, and its rapid cure when they are again eaten:
and the disease which is here so remarkably evident in its
symptoms, causes, and cure, is matched by numberless
other ailments, the causes of which, however, although
analogous, are less exactly known, and therefore less
easily combated.

2507 DIGESTION.

With regard to the quantity, too, as well as the kind of
food necessary, there will be much diversity in different
individuals. Dr. Dalton believed, from some experiments
which he performed, that the quantity of food necessary
for a healthy man, taking free exercise in the open air, is

as follows:—

Meat . . 4 - 16 ounces, or 1°00 lb. ayoird.

Bread . . erg ae ei ae Sera es
Butter or Fat .: : ot, 5 ae Cet as LA ee oot ey
Water : . or Sot ons. 3°86 125% -o.

The quantity of meat, however, here given, is probably
more in proportion to the other articles of diet enumerated
than is needful for the majority of individuals under the

circumstances stated.

PASSAGE OF FOOD THROUGH THE ALIMENTARY CANAL.

The course of the food through the alimentary canal of
man will be readily seen from the accompanying diagram
(fig. 66). The food taken into the mouth passes thence
through the cesophagus into the stomach, and from this
into the small and large intestine successively; gradually
losing, by absorption, the greater portion of its nutritive
constituents, The residue, together with such matters as
may have been added to it in its passage, is discharged
from the rectum through the anus.

We shall now consider, in detail, the process of diges-
tion, as it takes place in each stage of this journey of the
food through the alimentary canal.

The Salivary Glands and the Saliva..

The first of a series of changes to which the food is sub-
jected in the digestive canal, takes place in the cavity of
the mouth ; the solid articles of food are here submitted to
the action of the teeth (p. 59), whereby they are divided

SALIVARY GLANDS AND SALIVA. 257
and crushed, and by being at the same time mixed with
the fluids of the mouth, are reduced to a soft pulp, capable

Fig. 66.*

Pyloreas Ny

~
‘
cansyarsé Colon © we ©, Pancreas

S35)

se

ne

3

QQ
oo
ny
>‘

A

of being easily swallowed. The fluids with which the food
is mixed in the mouth consist of the secretion of the

* Fig. 66. Diagram of the alimentary canal. The smaii intestine
of man is from about 3 to 4 times as long as the /arge intestine

5

258 DIGESTION.

salivary glands, and the mucus secreted by the lining
membrane of the whole buccal cavity.

The glands concerned in the production of saliva, are
very extensive, and, in man and Mammalia generally, are
presented in the form of four pairs of large glands, the
parotid, submaxillary, sublingual, and numerous smaller
bodies, of similar structure and with separate ducts, which
are scattered thickly beneath the mucous membrane of the
lips, cheeks, soft palate, and root of the tongue. The
structure of all these glands is essentially the same. ach
is composed of several parts, called lobes, which are joined
together by areolar tissue; and each of these lobes, again,
is made up of a number of smaller parts, called lobules,
bound together as before by areolar tissue. Each of these
small divisions, called lobules, is a miniature representation
of the whole gland. It contains a small branch of the
duct, which, subdividing, ends in small vesicular pouches,
called acini, a group of which may be considered the

Fig. 67.*

dilated end of one of the smaller ducts (fig. 67). Each of
the acini is about =1,, of an inch in diameter, and is formed
of a fine structureless membrane, lined on the inner surface
and often filled by spheroidal or glandular epithelium;

Fig. 67. Diagram of a racemose or saccular compound gland; m,
entire gland, showing branched duct and lobular structure ; 7, a lobule
detached, with 0, branch of duct proceeding from it (after Sharpey).

SALIVA. 259

while on: the outside there is a plexus of capillary blood-
vessels. The accompanying diagram is intended to show
the typical structure of such glands as the salivary (fig. 67).

Saliva, as it commonly flows from the mouth, is mixed
with the secretion of the mucous membrane, and often
with air bubbles, which, being retained, by its viscidity,
make it frothy.

When obtained from the parotid ducts, and free from
mucus, saliva is a transparent watery fluid, the specific
gravity of which varies from 1°004 to 1:008, and in which,
when examined with the microscope, are found floating a
number of minute particles, derived from the secreting
ducts and vesicles of the glands. In the impure or mixed
saliva are found, besides:these particles, numerous epithelial
scales separated from the surface of the mucous membrane
of the mouth and tongue, and mucus-corpuscles, discharged
for the most part from the tonsils, which, when the saliva
is collected in a deep vessel, and left at rest, subside in the
form of a white opaque matter, leaving the supernatant
salivary fluid transparent and colourless, or with a pale
bluish-grey t'nt. In reaction, the saliva, when first secreted,
appears to be always alkaline; and_that from the parotid
gland is said to be more strongly alkaline than that from
the other salivary glands. This alkaline condition is most
evident when digestion is going on, and according to
Dr. Wright, the degree of alkalinity of the saliva bears a
direct proportion to the acidity of the gastric fluid secreted
at the same time. During fasting, the saliva, although
secreted alkaline, shortly becomes neutral; and it does so
especially when secreted slowly and allowed to mix with
the acid mucus of the mouth, by which its alkaline reaction
is neutralized.

The following analysis of the saliva is by Frerichs :—

260 __ DIGESTION.

Composition of Saliva.

Water . ‘ ; ; : : 994°I0
Solids ‘ ; ; ; ae 5S
Ptyalin . ; ; ; : 1°41
Fat ©). ‘ : . soos 0°07
Epithelium and Mucus . 5 2°13.
Salts :—
Sulpho-Cyanide of Potassium. i:
Phosphate of Soda
9 » Lime .
os », Magnesia . )2 ss
Chloride of Sodium .
4 », Potassium . ; 3
5°90

The rate at which saliva is secreted is subject to consider-
able variation. When the tongue and muscles concerned
in mastication are at rest, and the nerves of the mouth
are subject to no unusual stimulus, the quantity secreted is
not more than sufficient, with the mucus, to keep the mouth
moist. But the flow is much accelerated when the move-
ments of mastication take place, and especially when they
are combined with the presence of food in the mouth. It
may be excited also, even when the mouth is at rest, by
the mental impressions produced by the sight or thought
of food; also by the introduction of food into the stomach.
The influence of the latter circumstance was well shown in
a case mentioned by Dr. Gairdner, of a man whose pharynx
had been divided: the injection of a meal of broth into
the stomach was followed by the secretion of from six to
eight ounces of saliva.

Under these varying circumstances, the quantity of saliva
secreted in twenty-four hours varies also; its average
amount is probably from two to three pints in twenty-four
hours. In a man who had a fistulous opening of the
_ parotid duct, Mitscherlich found that the quantity of saliva
discharged from it during twenty-four hours, was from two

USES OF SALIVA. 261

to three ounces; and the saliva collected from the mouth
during the same period, and derived from the other sali-
vary glands, amounted to six times more than that from
the one parotid.

The purposes served by saliva are of several kinds. In the
first place, acting mechanically in conjunction with mucus,
it keeps the mouth in a due condition of moisture, facilitat-
ing the movements of the tongue in speaking, and the mas-
tication of food. (2:) It serves also in dissolving sapid
substances, and rendering them capable of exciting the
nerves of taste. But the principal mechanical purpose of
the saliva is, (3) that by mixing with the food during mas-
tication, it makes it a soft pulpy mass, such as may be
easily swallowed. To this purpose the saliva is adapted
both by quantity and quality. For, speaking generally,
the quantity secreted during feeding is in direct proportion
to the dryness and hardness of the food: as M. Lassaigne

-has shown, by a table of the quantity produced in the mas-
tication of a hundred parts of each of several kinds of food,
thirty parts suffice for a hundred parts of crumb of bread,
but not less than 120 for the crusts; 42°5 parts of saliva
are produced for the hundred of roast meat; 3:7 for as
much of apples; and so on, according to the general rule
above stated. The quality of saliva is equally adapted to
this end. It is easy to see how much more readily it mixes
with most kinds of food than water alone does; and M.
Bernard has shown that the saliva from the parotid, labial,
and other small glands, being more aqueous than the rest,
is that which chiefly braided and mixed with the food in
mastication ; while the more viscid mucoid secretion of the
submaxillary, palatine, and tonsillitic glands is spread over
the surface of the softened mass, to enable it to slide more
easily through the fauces and cesophagus. This view ob-
tains confirmation from the interesting fact pointed out by
Professor Owen, that in the great ant-eater, whose enor-
mously elongated tongue is kept moist by a large quantity

262 DIGESTION.

of viscid saliva, the submaxillary glands are remarkably
developed, while the parotids are not of unusual size.
Beyond these, its mechanical purposes, saliva performs
(4) a chemical part in the digestion of the food. When
saliva, or a portion of a salivary gland, or even a portion
of dried ptyalin, is added to starch paste, the starch is very
rapidly transformed into dextrin and grape-sugar; and
when common raw starch is masticated and mingled with
saliva, and kept with it at a temperature of 90° or 100°,
the starch-grains are cracked or eroded, and their contents
are transformed in the same manner as the starch-paste.
Changes similar to these are effected on the starch of fari-
naceous food (especially after cooking) in the stomach; and
it is reasonable to refer them to the action of the saliva, be-
cause the acid of the gastric fluid tends to retard or prevent,
rather than favour the transformation of the starch. It
may therefore be held, that:one purpose served by the
saliva in the digestive process is that of assisting in the
transformation of the starch, which enters so largely
into the composition of most articles of vegetable food,
and which (being naturally insoluble) is converted into
soluble dextrin and grape-sugar, and made fit for ab-

sorption.
Besides saliva, many azotized substances, especially if in

a state of incipient decomposition, may excite the trans-
formation of starch, such as pieces of the mucous mem-
brane of the mouth, bladder, rectum, and other parts,
various animal and vegetable tissues, and even morbid
products; but the gastric fluid will not produce the same
effect. The transformation in question is effected much
more rapidly by saliva, however, than by any of the other
fluids or substances experimented with, except the pan-
creatic secretion, which, as will be presently shown, is very
analogous to saliva. The actual process by which these
changes are effected is still obscure. Probably the azotized
substance, ptyalin, acts asa kind of ferment, like diastase

DEGLUTITION. ~ 263

in the process of malting, and excites molecular changes in
the starch which result in its transformation, first into
dextrin and then into sugar.

The majority of observers agree that the transformation
of starch into sugar ceases on the entrance of the food into
the stomach, or on the addition of gastric fluid to it in
a test-tube: while others maintain that it still goes on.
Probably all are right: for, although gastric fluid added
to saliva appears to arrest the action of the latter on
starch, yet portions of saliva mingled with food in mas-
tication may, for some time after their entrance into the
stomach, remain unneutralized by the gastric secretion,
and continue their influence upon the starchy principles
in contact with them.

Starch appears to be the only principle of food upon
which saliva acts chemically: it has no apparent influence
on any of the other ternary principles, such as sugar, gum,
cellulose, or (according to Bernard) on fat, and seems to be
equally destitute of power over albuminous and gelatinous
substances, so that we have as yet no information respect-
ing any purpose it can serve in the digestion of Carnivora,
beyond that of softening or macerating the food; though,
since such animals masticate their food very little, usually
‘bolting ”’ it, the saliva has probably but little use even in
this respect, in the process of digestion.

Passage of Food into the Stomach.

When properly masticated, the food is transmitted in
successive portions to the stomach by the act of deglutition
or swallowing. This act, for the purpose of description,
may be divided into three parts. In the first, particles of
food collected to a morsel glide between the surface of the
tongue and the palatine arch, till they have passed the |
anterior arch of the fauces; in the second, the morsel is |
carried through the pharynx; and in the third, it reaches

the stomach through the cesophagus. These three acts

264 DIGESTION.

follow each other rapidly. The first is performed volun-
tarily by the muscles of the tongue and cheeks. The second
also is effected with the aid of muscles which are in part
endued with voluntary motion, such as the muscles of the
soft palate and pharynx; but it is, nevertheless, an invo-
luntary act, and takes place without our being able to
prevent it, as soon as a morsel of food, drink, or saliva is
carried backwards to a certain point of the tongue’s sur-
face. When we appear to swallow voluntarily, we only
convey, through the first act of deglutition, a portion
of food or saliva beyond the anterior arch of the palate ;
then the substance acts as a stimulus, which, in accordance
with the laws of reflex movements hereafter to be described,
is carried by the sensitive nerves to the medulla oblongata,
when it is reflected by the motor nerves, and an involuntary
adapted action of the muscles of the palate and pharynx
ensues. ‘The third act of deglutition takes place in the
cesophagus, the muscular fibres of which are entirely beyond
the influence of the will.

The second act of deglutition is the most complicated,
because the food must pass by the posterior orifice of the
nose and the upper opening of the larynx without touching
them. When it has been brought, by the first act, between
the anterior arches of the palate, it is moved onwards by
the tongue being carried backwards, and by the muscles of
the anterior arches contracting on it and then behind it.
The root of the tongue being retracted, and the larynx
being raised with the pharynx and carried forwards under
the tongue, the epiglottis is pressed over the upper opening
of the larynx, and the morsel glides past it; the closure of
the glottis being additionally secured by the simultaneous
contraction of its own muscles: so that, even when the
epiglottis is destroyed, there is little danger of food or drink
passing into the larynx so long as its muscles can act freely.
At the same time the raising of the soft palate, so that its
posterior edge touches the back part of the pharynx, and

STRUCTURE OF THE STOMACH. 265

the approximation of the sides of the posterior palatine
arch, which move quickly inwards like side curtains, close
the passage into the upper part of the pharynx and the pos-
terior nares, and form an inclined plane, along the under
surface of which the morsel descends; then the pharynx,
raised up to receive it, in its turn contracts, and forces it
onwards into the cesophagus.

In the third act, in which the food passes through the
cesophagus, every part of that tube as it receives the morsel
and is dilated by it, is stimulated to contract: hence an
undulatory contraction of the cesophagus, which is easily
observable in horses while drinking, proceeds rapidly along
the tube. It is only when the morsels swallowed are large,
or taken too quickly in succession, that the progressive
contraction of the oesophagus is slow, and attended with
pain. Division of both pneumogastric nerves paralyzes the
contractile power of the cesophagus, and food accordingly
accumulates in the tube (Bernard).

DIGESTION OF FOOD IN THE STOMACH.
Structure of the Stomach.

It appears to be an almost universal character of animals,
that they have an internal cavity for the production of a
chemical change in the aliment—a cavity for digestion;
and when this cavity is compound, the part in which the
food undergoes its principal and most important changes is
the stomach.

In man and those Mammalia which are provided with a
single stomach, its walls consist of three distinct layers or,
coats, viz., an external peritoneal, an internal mucous,
and an intermediate muscular coat, with blood-vessels,
lymphatics, and nerves distributed in and between them.

The muscular coat of the stomach consists of three sepa-
rate layers or sets of fibres, which, according to their several
directions, are named the longitudinal, circular, and oblique.
The longitudinal set are the most superficial: they are con-

266 DIGESTION.

tinuous with the longitudinal fibres of the cesophagus, and
spread out in a diverging manner over the great end and
sides of the stomach, They extend as far as the pylorus,
being especially distinct at the lesser or upper curvature of
the stomach, along which they pass in several strong bands.
The next set are the circular or transverse fibres, which more
or less completely encircle all parts of the stomach; they
are most abundant at the middle and in the pyloric portion
of the organ, and form the chief part of the thick project-
ing ring of the pylorus. According to Pettigrew, these
fibres are not simple circles, but form double or figure-
of 8 loops, the fibres intersecting very obliquely. The next,
and consequently deepest set of fibres, are the oblique, con-
tinuous with the circular muscular fibres of the cesophagus,
and, according to Pettigrew, with the same double-looped
arrangement that prevails in the preceding layer: they
are comparatively few in number, and are placed only at
the cardiac orifice and portion of the stomach, over both
surfaces of which they are spread, some passing obliquely
from left to right; others from right to left, around the
cardiac orifice, to which, by their interlacing, they form a
kind of sphincter, continuous with that around the lower
end of the cesophagus. The fibres of which the several
muscular layers of the stomach, and of the intestinal canal
generally, are composed, belong to the class of organic
muscle, being composed of smooth or unstriped, elongated,
spindle-shaped fibre-cells; a fuller description of which
will be given under the head of Muscular Tissue.

The mucous membrane of the stomach, which rests upon
a layer of loose cellular membrane, or submucous tissue,
is smooth, level, soft, and velvety; of a pale pink colour
during life, and in the contracted state is thrown into
numerous, chiefly longitudinal, folds or rugze, which dis-
appear when the organ is distended.

In its general structure the mucous membrane of the
stomach resembles that of other parts (see Structure of
Mucous Membrane). But there are certain peculiarities

STRUCTURE OF THE STOMACH. 267

shared with the mucous membrane of the small and large
intestines, which, doubtless, are connected with the peculiar
functions, especially those relating to absorption, which
these parts of the alimentary canal perform.

Entering largely into the construction of the mucous mem-
brane, especially in the superficial part of the corium, is a
quantity of a very delicate kind of connective tissue, called
retiform tissue (fig. 72), or sometimes lymphoid or adenoid
tissue, because it so closely resembles that which forms the
stroma, or supporting framework of lymphatic glands (see
Section on Lymphatic Glands); the resemblance being
made much closer by the fact that the interspaces of this
retiform tissue are filled with corpuscles not to be distin-
guished from lymph-corpuscles.

At the deepest part of the mucous membrane, is a
layer of unstriped muscular fibres, called the muscularis
mucos@, which must not be confounded with the layers of
‘muscle constituting the proper muscular coat, and from
which it is separated by the submucous tissue. The mus-
cularis mucose is found in the cesophagus, as well as in
the stomach and intestines. |

When examined with a lens, the internal or free surface
of the stomach presents a. peculiar honeycomb appearance,
produced by shallow polygonal depressions or cells (fig. 68),
the diameter of which varies generally from 5},th to

200
+ioth of an inch; but near the pylorus is as much as -1,th
of an inch. They are separated by slightly elevated ridges,
which sometimes, especially in certain morbid states of the
stomach, bear minute, narrow, vascular processes, which
look like villi, and have given rise to the erroneous suppo-
sition that the stomach has absorbing villi, like those of
the small intestines. In the bottom of the cells minute
openings are visible (fig. 68), which are the orifices of per-
pendicularly arranged tubular glands (fig. 69) imbedded side
by side-in sets or bundles, in the substance of the mucous
membrane, and composing nearly the whole structure.

268 DIGESTION.

The glands which are found in the human stomach may
be divided into two classes, the tubular and lenticular.

Tubular Glands. The tubular
glands may be described as a col-
lection of cylinders with blind ex-
tremities, about =’, th of an inch in
length, and -1, in diameter, packed
closely together, with their long axis
at right angles to the surface of the
mucous membrane on which they
open, their blind ends resting on the submucous tissue.

Fig. 69.f (See fig. 69.) They
Surf. of are all composed of
ens ce, pDasement mem-

brane, and lined by
epithelial cells, but
ert they are not all

of exactly similar
shape; for while
some are simple
Dense straighttubes, open

areolar
tissue. at one end and
Sub-mucous

tissue of closed at the other
looser

texture. (fig. 69) j others

Transverse present at their
muscular we
fibres. deeper extremities

Longitudinal a Varicose, pouched,
muser, fibres. .
Peritoneum. OF In some Cases,

even a_ branched appearance (fig. 70, b and c). The

gris kato ete
LS ee Ee jak
a - ehele

* Fig. 68. Small portion of the surface of the mucous membrane of
the stomach (from Ecker) *.—The specimen shows the shallow de-
pressions, in each of which the smaller dark spots indicate the orifices
of a variable number of the gastric tubular glands. -

+ Fig. 69. Portion of human stomach (magnified 30 diameters, cut
vertically, both in a direction parallel to its long axis, and across it
(altered from Brinton).

GLANDS OF THE STOMACH. 269

epithelium lining them is not the same throughout. In
the upper third or fourth of their length it is cylindrical,

and continuous with that which covers the free mucous
surface of the rest of the stomach. In their lower part, on
the other hand, it is of the variety called glandular or sphe-
roidal, the cells being oval or somewhat. angular, and
about -!,,;th of an inch in diameter. The cells, however,
do not completely fill up the cavity of the gland which they
line, but leave a slight, central, thread-like space, the im-
mediate lining of which is a layer of small angular cells,
continuous with the cylindrical epithelium in the upper
portion of the tube. This description will become plain on
reference to fig. 71, which represents on a larger scale a
longitudinal section of one of the glands depicted in fig. 69.

* Fig. 7o. The gastric glands of the human stomach (magnified).
@, deep part of a pyloric gastric gland (from Kolliker) ; the cylindrical
epithelium is traceable to the cecal extremities. 6 and ¢, cardiac
gastric glands (from Allen Thompson) ; 3, vertical section of a smali
portion of the mucousmembrane with the glands magnified 30 diameters ;
c, deeper portion of one of the glands, magnified 65 diameters, showing
a slight division of the tubes, and a sacculated appearance, produced
‘by the large glandular cells within them ; d, cellular elements of the
cardiac glands magnified 250 diameters.

279 DIGESTION. «

In the greater number of the glands which are branched
at their deeper extremities, the spheroidal epithelium exists

Fig. 71.* in the divisions, while the main duct
and the upper part of the branches are
lined by the cylindrical variety (fig.
70, c). In the human stomach, ac-
cording to Dr. Brinton, the simple un-
divided tubes are the rule, and the
branched the exception.

The varieties in the epithelial cells
lining the different parts of the tubes,
correspond probably with differences
in the fluid secreted by their agency—
the cylinder-epithelium, like that on
the free surface of the stomach being
probably engaged in separating the
thin alkaline mucus which is always
present in greater or less quantity,
while the larger glandular cells probably secrete the proper
gastric juice.

Near the pylorus there exist glands branched at their
deep extremities, which are lined throughout by cylinder-
epithelium (fig. 70, a), and probably serve only for the
secretion of mucus. :

All the tubular glands, while they open by one end into
the cavity of the stomach, rest by their blind extremities
on a bed or matrix of areolar tissue (fig. 69), which is
prolonged upwards between them, so as to invest and
support them.

Lenticular glands.—Besides the cylindrical glands, there

* Fig. 71. Part of one of the gastric glands, highly magnified, to
show the arrangement of the epithelium in its interior ; a, columnar
cells lining the upper part of the tube; 0, small angular cells, into
which these merge below to form a central or axial layer within ; ¢, the
proper gastrie or glandular cells (after Brinton).

THE GASTRIC FLUID. 271

are also small closed sacs beneath the surface of the
mucous membrane, resembling exactly the solitary glands
of the intestine, to be described hereafter. Their num-
ber is very variable, and they are found chiefly along
the lesser curvature of the stomach, and in the pyloric
region, but they may be present in any part of the organ.
According to Dr. Brinton they are rarely absent in children.
Their function probably resembles that of the intestinal
solitary glands, but nothing is certainly known regarding it.

The blood-vessels of the stomach, which first break up
in the submucous tissue, send branches upward between
the closely packed glandular tubes, anastomosing around
them by means of a fine capillary network with oblong
meshes. Continuous with this deeper plexus, or prolonged
upwards from it, so to speak, is a more superficial network
of larger capillaries, which branch densely around the
orifices of the tubes, and form the framework on which are
moulded the small elevated ridges of mucous membrane
bounding the minute, polygonal pits before referred to.
From this superficial network the veins chiefly take their
origin. Thence passing down between the tubes, with no
very free connection with the deeper inter-tubular capillary
plexus, they open finally into the venous network in the
submucous tissue.

The nerves of the stomach are derived from the pneumo-
gastric and sympathetic.

Secretion and Properties of the Gastric Fluid.

While the stomach contains no food, and is inactive, no
gastric fluid is secreted; and mucus, which is either
neutral or slightly alkaline, covers its surface. But imme-
diately on the introduction of food or other foreign sub-
stance into the stomach, the mucous membrane, previously
quite pale, becomes slightly turgid and reddened with the
influx of a larger quantity of blood; the gastric glands
commence secreting actively, and an acid fluid is poured

272 DIGESTION.

out in minute drops, which gradually run together and flow
down the walls of the stomach, or soak into the substances
introduced. The quantity of this fluid secreted daily has
been variously estimated; but the average for a healthy
adult has been assumed to range from ten to twenty pints
in the twenty-four hours (Brinton).

The first accurate analysis of the gastric fluid was
made by Dr. Prout: but it does not appear that it was
collected in any large quantity, or pure and separate
from food, until the time when Dr. Beaumont was
enabled, by a fortunate circumstance, to obtain it from
the stomach of a man named St. Martin, in whom there
existed, as the result of a gunshot wound, an opening
leading directly into the stomach, near the upper extremity
of the great curvature, and three inches from the cardiac
orifice. The external opening was situate two inches
below the left mamma, in a line drawn from that part
to the spine of the left ilium. The borders of the
opening into the stomach, which was of considerable size,
had united, in healing, with the margins of the external
wound, but the cavity of the stomach was at last sepa-
rated from the exterior by a fold of mucous membrane,
which projected from the upper and back part of the
opening, and closed it like a valve, but could be pushed
back with the finger. The introduction of any mechanical
irritant, such as the bulb of a thermometer, into the
stomach, excited at once the secretion of gastric fluid.
This could be drawn off with a caoutchouc tube, and could
often be obtained to the extent of nearly an ounce. The
introduction of alimentary substances caused a much more
rapid and abundant secretion of pure gastric fluid than
the presence of other mechanical irritants did. No in-
crease of temperature could be detected during the most
active secretion; the thermometer introduced into the
stomach always stood at 100° Fahr., except during mus-
cular exertion, when the temperature of the, stomach, like

THE GASTRIC FLUID. 273

that of other parts of the body, rose one or two degrees
higher. .

M. Blondlot, and subsequently M. Bernard, and since
then, several others, by maintaining fistulous openings into
the stomachs of dogs, have confirmed most of the facts
discovered by Dr. Beaumont. And the man St. Martin
has frequently submitted to renewed experiments on his
stomach by various physiologists. From all these observa-
tions it appears, that pepper, salt, and other soluble
stimulants, excite a more rapid discharge of gastric fluid
than mechanical irritation does; so do alkalies generally,
but acids have a contrary effect. When mechanical irri-
tation is carried beyond certain limits so as to produce
pain, the secretion, instead of being more abundant,
diminishes or ceases entirely, and a ropy mucus is poured
out instead. Very cold water, or small pieces of ice, at
first render the mucous membrane pallid, but soon a kind
of reaction ensues, the membrane becomes turgid with
blood, and a larger quantity of gastric juice is poured out.
The application of too much ice is attended by diminution
in the quantity of fluid secreted, and by consequent re-
tardation of the process of digestion. The quantity of the
secretion seems to be influenced also by impressions made
on the mouth; for Blondlot found that when sugar was
introduced into the dog’s stomach, either alone, or mixed
with human saliva, a very small secretion ensued: but
when the dog had himself masticated and swallowed it,
the secretion was abundant.

Dr. Beaumont described the secretion of the human
stomach as ‘“‘a clear transparent fluid, inodorous, a little
saltish, and very perceptibly acid. Its taste is similar to

that of thin mucilaginous water, slightly acidulated with.

muriatic acid, It is readily diffusible in water, wine, or
spirits; slightly effervesces with alkalies; and is an eflec-

tual solvent of the materia alimentaria. It possesses the
=z

|

274 DIGESTION.

property of coagulating albumen in an eminent degree ;
is powerfully antiseptic, checking the putrefaction of meat ;
and effectually restorative of healthy action, when applied
to old feetid sores and foul ulcerating surfaces.”

The chemical composition of the gastric juice of the
human subject has been particularly investigated by
Schmidt, a favourable case for his doing so occurring in
the person of a peasant named Catherine Kiitt, aged 35,
who for three years had had a gastric fistula under the left
mammary gland, between the cartilages of the ninth and
tenth ribs.

The fluid was obtained by putting into the stomach
some hard indigestible matter, as dry peas, and a little
water, by which means the stomach was excited to secre-
tion, at the same time that the matter introduced did
not complicate the analysis by being digested in the fluid
secreted. The gastric juice was drawn off wisn an:
elastic tube inserted into the fistula.

The fluid thus obtained was acid, limpid, and odourless,
with a mawkish taste. Its density varied from 1:0022 to
1°0024. Under the microscope a few cells from the gastric
glands and some fine granular matter were observable.

The following table gives the mean of two analyses of
the above-mentioned fluid; and arranged by the side of it,
for purposes of comparison, is an analysis of gastric juice
from the sheep and dog.

COMPOSITION OF GASTRIC FLUID. 275

Composition of Gastric Juice.

Human Sheep’s Dog’s
Gastric Juice. Gastric Juice. Gastric Juice.

Water 3 x i 99440 986° 14. Q71°17

Solid Constituents . 5°59 13°85 28°82
eienent: Pepsin (with

a trace of Ammonia) . 3°19 4°20 17°50

Hydrochloric Acid ~- 6:39 1°55 2°70

‘Solids / Chloride of Calcium . 0°06 Oul 1°66

‘Be Sodium . 1°46 4:36 =|

» Potassium . 0°55 1°51 1'07
Phosphate of Lime,

Magnesia, and Iron . 0712 2°09 2°73

~

In all the above analyses the amount of water given
must be reckoned as rather too much, inasmuch as a cer-
tain quantity of saliva was mixed with the gastric fluid.
The allowance, however, to be made on this account is
only very small.

Considerable difference of opinion has existed concern-
ing the natur2 of the free acid contained in the gastric
juice, chiefly whether it is hydrochloric or lactic. The
weight of evidence, however, is in favour of free hydro-
chloric acid, being that to which, in the human subject, the
acidity of the gastric fluid is mainly due; although there
is no doubt that others, as lactic, acetic, butyric, are not
-unfrequently to be found therein.

The animal matter mentioned in the analysis of the gas-
tric fluid is named pepsin, from its power in the process
of digestion. It is an azotised substance, and is best pro-
cured by digesting portions of the mucous membrane of
the stomach in cold water, after they have been macerated
for some time in water at a temperature between 80° and
100° F. The warm water dissolves various substances as
well as some of the pepsin, but the cold water takes up

little else than pepsin, which, on evaporating the cold
T 2

276 DIGESTION.

solution, is obtained in a greyish-brown viscid fluid. The
addition of alcohol throws down the pepsin in greyish-
white flocculi ; and one part of the principle thus prepared,
if dissolved in even 60,000 parts of water, will digest meat.
and other alimentary substances.

‘The digestive power of the gastric fluid is manifested in its
softening, reducing into pulp, and partially or completely
dissolving various articles of food placed in it at a tempe-
rature of from 90° to 100°. This, its peculiar property,
requires the presence of both the pepsin and the acid;
neither of them can digest alone, and when they are
mixed, either the decomposition of the pepsin, or the
neutralization of the acid, at once destroys the digestive
property of the fluid. For the perfection of the process
also, certain conditions are required, which are all found
in the stomach; namely (1), a temperature of about
100° F.; (2), such movements as the food is subjected to
by the muscular actions of the stomach, which bring in
succession every part of it in contact with the mucous
membrane, whence the fresh gastric fluid is being secreted;
(3), the constant removal of those portions of food which
are already digested, so that what remains undigested may
be brought more completely into contact with the solvent
fluid; and (4) a state of softness and minute division, such
as that to which the food is reduced by mastication previous
to its introduction into the stomach.

The chief circumstances connected with the mode in
which the gastric fluid acts upon food during natural diges-
tion, have been determined by watching its operations
when removed from the stomach and placed in conditions
as nearly as possible like those under which it acts while
within that viscus. The fact that solid food, immersed in
gastric fluid out of the body, and kept at a temperature of
about 100°, is gradually converted. into a thick fluid similar
to chyme, was shown by Spallanzani, Dr. Stevens, Tiede-
mann and Gmelin and others. They used the gastric fluid —

DIGESTIVE POWER OF GASTRIC FLUID. 277

‘of dogs, obtained by causing the animals to swallow small
pieces of sponge, which were subsequently withdrawn,
soaked with the fluid—and proved nearly as much as the
latter experiments of the same kind of gastric fluid by
Blondlot, Bernard, and others. But these need not be
particularly referred to, while we have the more satisfac-
tory and instructive observations which Dr. Beaumont
made with the fluid obtained from the stomach of St.
Martin. After the man had fasted seventeen hours,
Dr. Beaumont took one ounce of gastric fluid, put into it a
solid piece of boiled recently salted beef weighing three
drachms, and placed the vessel which contained them in a
water bath heated to 100°. ‘In forty minutes digestion
had distinctly commenced over the surface of the meat; in
fifty minutes, the fluid had become quite opaque and
cloudy, the external texture began to separate and become
loose; and in sixty minutes chyme began to form. At
I p.m.” (two hours after the commencement of the experi-
ment) ‘‘the cellular texture seemed to be entirely
destroyed, leaving the muscular fibres loose and uncon-
nected, floating about in small fine shreds, very tender and
soft.” In six hours, they were nearly all digested—a few
fibres only remaining. After the lapse of ten hours, every
part of the meat was completely digested. The gastric
juice, which was at first transparent, was now about the
colour of whey, and deposited a fine sediment of the colour
of meat. A similar piece of beef was, at the time of the
commencement of this experiment, suspended in the
stomach by means of a thread: at the expiration of the
first hour it was changed in about the same degree as the
meat digested artificially; but at the end of the second ~
hour, it was completely digested and gone.

It other experiments, Dr. Beaumont withdrew through
the opening of the stomach some of the food which had
‘been taken twenty minutes previously, and which was
completely mixed with the gastric juice. He continued

278 | DIGESTION.

the digestion, which had already commenced, by means of
artificial heat in a water-bath. In a few hours the food
thus treated was completely chymified; and the artificial
seemed in this, as in several other experiments, to be
exactly similar to, though a little slower than, the natural
digestion.

The apparent identity of the process in- and outside of
the stomach thus manifested, while it shows that we may
regard digestion as essentially a chemical process, when
once the gastric fluid is formed, justifies the belief that
Dr. Beaumont’s other experiments with the digestive fluid
may exactly represent the modifications to which, under
similar conditions, its action in the stomach would be
liable. He found that, if the mixture of food and gastric
fluid were exposed to a temperature of 34° F., the process
of digestion was completely arrested. In another experi-
ment, a piece of meat which had been macerated in water
at a temperature of 100° for several days, till it acquired
a strong putrid odour, lost, on the addition of some fresh
gastric juice, all signs of putrefaction, and soon began to
be digested. From other experiments he obtained the
data for estimates of the degrees of digestibility of various
articles of food, and of the ways in which the digestion is
liable to be affected, to which reference will again be
made.

When natural gastric juice cannot be obtained, many
of these experiments may be performed with an artificial
’ digestive fluid, the action of which, probably, very closely
resembles that of the fluid secreted by the stomach. It is
made by macerating in water portions of fresh or recently
dried mucous membrane of the stomach of a pig * or other
omnivorous animal, or of the fourth stomach of the calf,

* The best portion of the stomach of the pig for this purpose is that
between the cardiac and pyloric orifices; the cardiac portion appears
to furnish the least active digestive fluid.

a

’

ARTIFICIAL DIGESTION, 279

and adding to the infusion a few drops of hydrochloric
acid—about 3°3 grains to half an ounce of the mixture,
according to Schwann. Portions of food placed in such
fluid, and maintained with it at. a temperature of about —
100, are, in an hour or more, according to the toughness
of the substance, softened and changed in just the same
manner as they would be in the stomach.

The nature of the action by which the mucous mem-
brane of the stomach and its secretion work these changes
in organic matter is exceedingly obscure. The action of
the pepsin may be compared with that of a ferment, which
at the same time that it undergoes change itself, induces
certain changes also in the organic matters with which it
isin contact. Or its mode of action may belong to that
class of chemical processes termed “catalytic,” in which
a substance excites, by its mere presence, and without
itself undergoing change as ordinary ferments do, some
chemical action in the substances with which it is in
contact. So, for example, spongy platinum, or charcoal,
placed in a mixture, however voluminous, of oxygen and
hydrogen, makes them combine to form water; and
diastase makes the starch in grains undergo transforma-
tion, and sugar is produced. And that pepsin acts in
some such manner appears probable from the very minute
quantity capable of exerting the peculiar digestive action
on a large quantity of food, and apparently with little
diminution in its active power. The process differs from
ordinary fermentation, it being unattended with the for-
mation of carbonic acid, in not requiring the presence of
oxygen, and in being unaccompanied by the production of
new quantities of the active principle, or ferment. It
agrees with the processes of both fermentation and organic
catalysis, in that whatever alters the composition of the |
pepsin (such as heat above 100°, strong alcohol, or strong
acids), destroys the digestive power of the fluid.

280 ’ DIGESTION.

Changes of the Food in the Stomach. .

The general effect of digestion in the stomach is the
conversion of the food into chyme, a substance of various
composition according to the nature of the food, yet always
presenting a characteristic thick, pultaceous, grumous con-
sistence, with the undigested portions of the food mixed
- ina more fluid substance, and a strong, disagreeable acid
odour and taste. Its colour depends on the nature of the
food, or on the admixture of yellow or green bile which
may, apparently, even in health, pass into the stomach.

Reduced into such a substance, all the various materials
of a meal may be mingled together, and near the end of
the digestive process hardly admit of recognition; but the
experiments of artificial digestion, and the examination of
stomachs with fistule, have illustrated many of the changes
through which the chief alimentary principles pass, and
the times and modes in which they are severally disposed
of. These must now be traced.

The readiness with which the gastric fluid acts on the

several articles of food is, in some measure, determined by
the state of division, and the tenderness and moisture of
the substance presented to it. By minute division of the
food, the extent of surface with which the digestive fluid
can come in contact is increased, and its action proportion-
ably accelerated. Tender and moist substances offer less
resistance to the action of the gastric juice than tough,
hard, and dry ones do, because they may be thoroughly
penetrated by it, and thus be attacked not only at the
surface, but at every part at once. The readiness with

which a substance is acted upon by the gastric fluid does.

not, however, necessarily imply the degree of its nutritive

property ; for a substance may be nutritious, yet, on
account of its toughness and other qualities, hard to
digest; and many soft, easily digested substances contain
comparatively a small amount of nutriment.. But for a

Sal sheet oe ae eS! ese wf:

’
’

DIGESTION OF FOOD IN THE STOMACH. 281

substance to be nutritive, it must be capable of being
assimilated to the blood; and to find its way into the
blood, it must, if insoluble, be digestible by the gastric
fluid or some other secretion in the intestinal canal. There
is, therefore, thus far, a necessary connection between the
digestibility of a substance and its power of affording
nutriment.

Those portions of food which are liquid when taken into
the stomach, or which are easily soluble in the fluids
therein, are probably at once absorbed by the blood-
vessels in the mucous membrane of the stomach. Magen-
die’s experiments, and better still, those of Dr. Beaumont,
have proved this quick absorption of water, wine, weak
saline solutions, and the like; that they are absorbed
without manifest change by the digestive fluid, and that,
generally, the water of such liquid food as soups is
absorbed at once, so that the substances suspended in it
are concentrated into a thicker material, like the chyme
from solid food, before the digestive fluid acts upon them.

The action of the gastric fluid on the several kinds of solid
food has been studied in various ways. In the earliest
experiments, perforated metallic and glass tubes, filled
with the alimentary substances, were introduced into the
stomachs of animals, and after the lapse of a certain time
withdrawn, to observe the condition of the contained sub-
stances; but such experiments are fallacious, because
gastric fluid has not ready access to the food. A better
method was practised in a series of experiments by Tiede-
mann and Gmelin, who fed dogs with different substances,
and killed them in a certain number of hours afterwards.
But the results they obtained are of less interest than
those of the experiments of Dr. Beaumont on his patient,
St. Martin, and of Dr. Gosse, who had the power of
vomiting at will.

Dr. Beaumont’s observations show, that the process of
digestion in the stomach, during health, takes place so

282 ; DIGESTION,

rapidly, that a full meal, consisting of animal and vege-
table substances, may nearly all be converted into chyme
in about an hour, and the stomach left empty in two hours
and a half. The details of two days’ experiments will be
sufficient examples :—

_ Exp. 42.—April 7th, 8 a.m. St. Martin breakfasted on
three hard-boiled eggs, pancakes, and coffee. At half-past
eight o’clock, Dr. Beaumont examined the stomach, and
found a heterogeneous mixture of the several articles

slightly digested. .... At a quartar past ten, no part of

the breakfast remained in the stomach.

Exp. 43.—At eleven o’clock the same day, he ate two
roasted eggs and three ripe apples. In half an hour they
were in an incipient state of digestion; and a quarter’ past
twelve no vestige of them remained.

Exp. 44.—At two o’clock p.m. the same day, he dined
on roasted pig and vegetables. At three o’clock they were
half chymified, and at half-past four nothing remained but
a very little gastric juice. |

Again, Exp. 46.—April 9th. At three o’clock p.m. he

dined on boiled dried codfish, potatoes, parsnips, bread,.

and drawn butter. At half-past three o’clock examined,
and took out a portion about half digested; the potatoes.
the least so. The fish was broken down into small
filaments; the bread and parsnips were not to be dis-
tinguished. At four o’clock, examined another portion.

Very few particles of fish remained entire. Some of the ©

few potatoes were distinctly to be seen. At. half-past four

o’clock, he took out and examined another portion; all ©

completely chymified. At five o’clock stomach empty.
Many circumstances besides the nature of the food are
apt to influence the process of chymification. Among them
are, the quantity of food taken; the stomach should be
fairly filled, not distended: the time that has elapsed since
the last meal, which should be at least enough for the
stomach to be quite clear of food: the amount of exercise.

ee —

» ET

pees

/

DIGESTION IN THE STOMACH. 283

previous and subsequent to the meal, gentle exercise being
favourable, over-exertion injurious to digestion; the state
of mind—tranquillity of temper being apparently essential
to a quick and due digestion: the bodily health: the state
of the weather. But under ordinary circumstances, from
three to four hours may be taken as the average time
occupied by the digestion of a meal in the stomach.

Dr, Beaumont constructed a table showing the times
required for the digestion of all usual articles of food in
St. Martin’s stomach, and in his gastric fluid taken from
the stomach. Among the substances most quickly digested
were rice and tripe, both of which were chymified in an
hour; eggs, salmon, trout, apples, and venison, were
digested in an hour and a half; tapioca, barley, milk,
liver, fish, in two hours; turkey, lamb, potatoes, pig, in
two hours and a half; beef and mutton required from
three hours to three and a half, and both were more

digestible than veal ; fowls were like mutton in their degree

of digestibility. Animal substances were, in general, con-
verted into chyme more rapidly than vegetables.

Dr. Beaumont’s experiments were all made on ordinary
articles of food. A minuter examination of the changes
produced by gastric digestion on various tissues has been
made by Dr. Rawitz, who examined microscopically the
product of the artificial digestion of different kinds of
food, and the contents of the feeces after eating the same
kinds of food. The general results of his examinations,
as regards animal food, show that muscular tissue breaks
up into its constituent fasciculi, and that these again are
divided transversely ; gradually the transverse striee become
indistinct, and then disappear ; and finally; the sarcolemma
seems to be dissolved, and no trace of the tissue can be
found in the chyme, except a few fragments of fibres.
These changes ensue most rapidly in the flesh of fish and
hares, less rapidly in that of poultry and other animals.
The cells of cartilage and fibro-cartilage, except those of fish,

284 DIGESTION.

pass unchanged through the stomach and intestines, and
may be found in the feces. ‘The interstitial tissues of these
structures are converted into pulpy textureless substances
in the artificial digestive fluid, and are not discoverable in
the feeces. Elastic fibres are unchanged in the digestive
fluid. Fat-cells are sometimes found quite unaltered in the
feeces : and crystals of cholesterin may usually be obtained
from feces, especially after the use of pork fat.

As regards vegetable substances, Dr. Rawitz states, that
he frequently found large quantities of cell-membranes un-
changed in the feces; also starch-cells, commonly deprived
of only part of their contents. The green colouring prin-
ciple, chlorophyll, was usually unchanged. The walls of
the sap-vessels and spiral vessels were quite unaltered by
the digestive fluid, and were usually found in large
quantities in the feces; their contents, probaby, were
‘removed.

From these experiments, we may understand the structural
changes which the chief alimentary substances undergo in
their conversion into chyme; and the proportions of each
which are not reducible to chyme, nor capable of any
further act of digestion. The chemical changes undergone
in and by the proximate principles are less easily traced.

Of the albuminous principles, some, as the casein of milk,
are coagulated by the acid of the gastric fluid; and thus,
before they are digested, come into the condition of the
other solid principles of the food. These, including solid
albumen and fibrin, in the same proportion that they are
broken up and anatomically disorganized by the gastric
fluid, appear to be reduced or lowered in their chemical
composition. This chemical change is probably produced,
as suggested by Dr. Prout, by the principles entering into
combination with water. It is sufficient to conceal nearly
all their characteristic properties; the albumen is rendered
scarcely coagulable by heat; the gelatin, even when its
solution is evaporated, does not congeal in cooling; the

oe

gee ale ee a a Ce a alm lL

DIGESTION IN THE STOMACH. 285

fibrin and casein cannot be found by their characteristic
tests. It would seem, indeed, that ail these various sub-
stances are converted into one and the same principle, ‘a
low form of albumen, not precipitable by nitric acid or heat,
and now generally termed albuminose or peptone, from which,
after being absorbed, they are again raised, in the elabora-
tion of the blood, to which they are ultimately assimilated.

The change of molecular constitution suffered by the
albuminous parts of the food, in consequence of the action
of the gastric juice, has an important relation to their
absorption by the blood-vessels of the stomach. From the
condition of ‘ colloids,’ or substances, so named by Profes-
sor Graham, which are absorbed with extreme difficulty,
they appear, from experiments of Funke, to assume to a
great degree the character of ‘crystalloids,’ which can
pass through animal membranes with ease.*

Whatever be the mode in which the gastric secretion
affects these principles, it, or something like it, appears
essential, in order that they may be assimilated to the
blood and tissues. For, when Bernard and Barreswil in-
jected albumen dissolved in water into the jugular veins
of dogs, they always, in about three hours after, found it
in the urine. But if, previous to injection, it was mixed
with gastric fluid, no trace of it could be detected in the
urine. The influence of the liver seems to be almost as
efficacious as that of the gastric fluid, in rendering albu-
men assimilable; for Bernard found that, if diluted ege-
albumen, unmixed with gastric fluid, is injected into the
portal vein, it no longer makes its appearance in the urine,
and is, therefore, no doubt, assimilated by the blood.

_Probably, most of the albuminose, with other soluble |
and fluid materials, is absorbed directly from the stomach |

by the minute blood-vessels with which the mucous mem-
brane is so abundantly supplied.

* These terms will be further explained and illustrated in the Chapter
on Absorption,

286 7 DIGESTION.

The saccharine including the amylaceous principles are at
first, probably, only mechanically separated from the vege-
table substances within which they are contained, by the
action of the gastric fluid. The soluble portions, viz.,
dextrin and sugar, are probably at once absorbed. The
insoluble ones, viz., starch and lignin, (or some parts of
them) are rendered soluble and capable of absorption, by
being converted into dextrin or grape-sugar. It is pro-
bable that this change is carried on to some extent in
the stomach; but this conversion of starch into sugar is
effected, not by the gastric fluid, but by the saliva intro-
duced with the food, or subsequently swallowed. The
transformation of starch is continued in the intestinal
canal, as will be shown, by the secretion of the pancreas,
and perhaps by that of the intestinal glands and mucous
membrane. The power of digesting uncooked starch is,
however, very limited in man and Carnivora, for when
starch has been taken raw, as in corn and rice, large
quantities of the granules are passed unaltered with the
excrements. Cooking, by expanding or bursting the
envelopes of the granules, renders their interior more
amenable to the action of the digestive organs; and the
abundant nutriment furnished by bread, and the large
proportion that is absorbed of the weight consumed, afford

proof of the completeness of their power to make its starch |

soluble and prepare it for absorption.

Of the oleaginous principles,—as to their changes in the
stomach, no more can be said than that they appear to be
reduced to minute particles, and pass into the intestines
mingled with the other constituents of the chyme. In the
case of the solid fats, this effect is probably produced by
the solvent action of the gastric juice on the areolar tissue,
albuminous cell-walls, &c., which enter into their com-

position, and by the solution of which the true fat is able-

to mingle more uniformly with the other constituents of
the chyme. Being further changed in the intestinal canal,
fat is rendered capable of absorption by the lacteals.

_ MOVEMENTS IN THE STOMACH. 287

Movements of the Stomach.

It has been already said, that the gastric fluid is assisted
in accomplishing its share in digestion by the movements
of the stomach. In granivorous birds, for example, the
contraction of the strong muscular gizzard affords a neces-
sary aid to digestion, by grinding and triturating the
hard seeds which constitute part of the food. But in the
stomachs of man and Mammalia the motions of the mus-
cular coat are too feeble to exercise any such mechanical
force on the food; neither are they needed, for mastication
has already done the mechanical work of a gizzard; and
the experiments of Réaumur and Spallanzani have demon-
strated that substances enclosed in perforated tubes, and
consequently protected from mechanical influence, are yet
digested.

The normal actions of the muscular fibres of the human
stomach appear to have a three-fold purpose; first, to
adapt the stomach to the quantity of food in it, so that its
walls may be in contact with the food on all sides, and, at
the same time, may exercise a certain amount of com-
pression upon it; secondly, to keep the- orifices of the
stomach closed until the food is digested; and, thirdly, to
perform certain peristaltic movements, whereby the food,
as it becomes chymified, is gradually propelled towards,
and ultimately through, the pylorus. In accomplishing
this latter end, the movements without doubt materially
contribute towards effecting a.thorough intermingling of
the food and the gastric fluid.

When digestion is not going on, the stomach is uniformly
contracted, its orifices not more firmly than the rest of its.
walls; but, if examined shortly after the introduction of
food, it is found closely encircling its contents, and its ori-

fices are firmly closed like sphincters. The cardiac orifice,

every time food is swallowed, opens to admit its passage
to the stomach, and immediately again closes. The pyloric
orifice, during the first part of gastric digestion, is usually

288 DIGESTION.

.

so completely closed, that even when the stomach is sepa-
rated from the intestines, none of its contents escape. But
towards the termination of the digestive process, the
pylorus seems to offer less resistance to the passage of
substances from the stomach; first it yields to allow the
successively digested portions to go through it; and then
it allows the transit of even undigested substances. }

From the observations of Dr. Beaumont on the man St.
Martin, it appears that food, so soon as it enters the
stomach, is subjected to a kind of peristaltic action of the
muscular coat, whereby the digested portions are gradually
approximated towards the pylorus. The movements were
observed to increase in rapidity as the process of chymifica-
tion advanced, and were continued until it was completed.

The contraction of the fibres situated towards the pyloric
end of the stomach seems to. be more energetic and more
decidedly peristaltic than those of the cardiac portion.
Thus, Dr. Beaumont found that when the bulb of the
thermometer was placed about three inches from the
pylorus, it was tightly embraced from time to time and
drawn towards the pyloric orifice for a distance of three or
four inches. The object of this movement appears to be,
as just said, to carry the food towards the pylorus as, fast
as it is formed into chyme, and to propel the chyme into
the duodenum; the undigested portions of food being
kept back until they are also reduced into chyme, or until
all that is digestible has passed out. The action of these
fibres is often seen in the contracted state of the pyloric
portion of the stomach after death, when it alone is con-
tracted and firm, while the cardiac portion forms a dilated
sac. Sometimes, by a predominant action of strong circular
fibres placed between the cardia and pylorus, the two por-
tions, or ends as they are called, of the stomach, are separated
from each other by a kind of hour-glass contraction.

The interesting researches of Dr. Brinton have clearly
' established that, by means of this peristaltic action of the

MOVEMENTS OF THE STOMACH. 289

muscular coats of the stomach, not merely is chymified
food gradually propelled through the pylorus, but a kind
of double current is continually kept up among the con-
tents of the stomach, the circumferential parts of the mass
being gradually moved onward towards the pylorus by
the peristaltic contraction of the muscular fibres, while the
central portions are propelled in the opposite direction,
namely, towards the cardiac orifice ; in this way is kept up
a constant circulation of the contents of the viscus, highly
conducive to their free mixture with the gastric fluid and
to their ready digestion.

These actions of the stomach are peculiar to it and inde-
pendent. But it is, also, adapted to act in concert with
the abdominal muscles, in certain circumstances which can
hardly be called abnormal, as in vomiting and eructation.
It has indeed been frequently stated that the stomach
itself is quite passive during vomiting, and that the ex-
pulsion of its contents is effected solely by the pressure
exerted upon it when the capacity of the abdomen is
diminished by the contraction of the diaphragm, and sub-
sequently of tne abdominal muscles. The experiments
and observations, however, which are supposed to confirm
this statement, only show that the contraction of the abdo-
minal muscles alone is sufficient to expel matters from an
unresisting bag through the cesophagus; and that, under
very abnormal circumstances, the stomach, by itself, cannot
or rather does not expel its contents. They by no means
show that in ordinary vomiting the stomach is passive ;
and, on the other hand, there are good reasons for believing
the contrary.

It is true that facts are wanting to demonstrate with
certainty this action of the stomach in vomiting; but some
of the cases of fistulous opening into the organ appear
to support the belief that it does take place;* and the

* A collection of cases of fistulous communication with the stomach,
through the abdominal parietes, has been given by Dr. Murchison in
vol, xli, of the Medico-Chirurgical Transactions. U

290° DIGESTION. ©

analogy of the case of the stomach with that of the other
hollow viscera, as the rectum and bladder, may be also
cited in confirmation.

Besides the influence which it may thus have by its con-
traction, the stomach also essentially contributes to the act
of vomiting, by the contraction of its pyloric orifice at the
same time that the oblique fibres around the cardiac orifice
are relaxed. For, until the relaxation of these fibres, no
vomiting can ensue; when contracted, they can as well
resist all the force of the contracting abdominal and other
muscles, as the muscles by which the glottis is closed can
resist the same force in the act of straining. Doubtless
we may refer many of the acts of retching and ineffectual
attempts to vomit, to the want of concord between the
relaxation of these muscles and the contraction of the
others. |

The muscles with which the stomach co-operates in con-
traction during vomiting, are chiefly and primarily those
of the abdomen; the diaphragm also acts, but not as the
muscles of the abdominal walls do. They contract and
compress the stomach more and more towards the back
and upper parts of the diaphragm; and the diaphragm
(which is usually drawn down in the deep inspiration that
precedes each act of vomiting) holds itself fixed in contrac-
tion, and presents an unyielding surface against which the
stomach may be pressed. It is enabled to act thus, and
probably only thus, because the inspiration which precedes
the act of vomiting is terminated by the closure of the glottis;
after which the diaphragm can neither descend further,
except by expanding the air in the lungs, nor, except by
compressing the air, ascend again until, the act of vomiting
having ceased, the glottis is opened again (see diagram,
p- 231; see also p. 233).

Some persons possess the power of vomiting at will,
without applying any undue irritation to the stomach, but
simply by a voluntary effort. It seems also, that this
power may be acquired by those who do not naturally

HUNGER AND THIRST. 291

possess it, and by continual practice may become a habit.
There are cases also of rare occurrence in which persons
habitually swallow their food hastily, and nearly unmasti-
eated, and then at their leisure regurgitate it, piece by
piece, into their mouth, remasticate, and again swallow it,
exactly as is done by the ruminant order of Mammalia.

Influence of the Nervous System on Gastric Digestion.

This influence is manifold ; and is evidenced, Ist, in the
sensations which induce to the taking of food ; 2nd, in the
secretion of the gastric fluid; 3rd, in the movements of the
food in and from the stomach.

The sensation of hunger is manifested in consequence of
deficiency of food in the system. The mind refers the
sensation to the stomach; yet since the sensation is relieved
by the introduction of food either into the stomach itself,
or into the blood through other channels than the stomach,
it would appear not to depend on the state of the stomach
alone. This view is confirmed by the fact, that the divi-

[Diab

sion of both pneumogastric nerves, which are the principal.

channels by which the mind is cognisant of the condition
of the stomach, does not appear to allay the sensations of
hunger.

But that the stomach has some share in this sensation
is proved by the relief afforded, though only temporarily,
by the introduction of even non-alimentary substances into
this organ. It may, therefore, be said that the sensation
of hunger is derived from the system generally, but chiefly
from the condition of the stomach, the nerves of which,
we may suppose, are more affected by the state of the in-
sufficiently replenished blood than those of other organs
are. .

The sensation of thirst, indicating the want of fluid, is
referred to the fauces, although, as in hunger, this is
merely the local declaration of a general condition existing
in the system. For thirst is relieved for only a very short

U2

-_

AR

‘

292 DIGESTION.

time by moistening the dry fauces; but may be relieved
completely by the introduction of liquids into the blood,
either through the stomach, or by injections into the
blood-vessels, or by absorption from the surface of the
skin or the intestines. The sensation of thirst is per-
ceived most naturally whenever there is a disproportion-
ately small quantity of water in the blood: as well,
therefore, when water has been abstracted from the blood,
as when saline or any solid matters have been abundantly
added to it. Wecan express the fact (even if it be not
an explanation of it), by saying that the nerves of the
mouth and fauces, through which the sense of thirst is
chiefly derived, are more sensitive to this condition of the
blood than other nerves are. And the cases of hunger
and thirst are not the only ones in which the mind derives,
from certain organs, a peculiar predominant sensation of
some condition affecting the whole body. Thus, the sensa-
. tion of the “ necessity of breathing,”’ is referred especially
to the lungs; but, as Volkmann’s experiments show, it
depends on the condition of the blood, which circulates
everywhere, and is felt even after the lungs of animals
are removed; for they continue, even then, to gasp and
manifest the sensation of want of breath. And, as with
respiration when the lungs are removed, the mind may
still feel the body’s want of breath; so in hunger and
thirst, even when the stomach has been filled with innu-
tritious substances, or the pneumogastric nerves have
been divided, and the mouth and fauces are kept moist,
the mind is still aware, by the more obscure sensations in
other parts, of the whole body’s need of food and
water. .

The influence of the nervous system on the secretion of gastric.
fluid, is shown plainly enough in the influence of the mind
upon digestion in the stomach ; and is, in this regard, well
illustrated by several of Dr. Beaumont’s observations.
M. Bernard also, watching the act of gastric digestion in.

INFLUENCE OF THE NERVOUS SYSTEM. ® 293

dogs which had fistulous openings into their stomachs,
saw that on the instant of dividing their pneumogastric
nerves, the process of digestion was stopped, and the
mucuous membrane of the stomach, previously turgid with
‘blood, became pale, and ceased to secrete. These, how-
ever, and the like experiments showing the instant effect
of division of the pneumogastric nerves, may prove no
more than the effect of a severe shock, and the fact that
influences affecting digestion may be conveyed to the
stomach through those nerves. From other experiments
it may be gathered, that although, as in M. Bernard’s,
the division of both pneumogastric nerves always tem-
porarily suspends the secretion of gastric fluid, and so
arrests the process of digestion, and is occasionally followed
by death from inanition; yet the digestive powers of the
stomach may be completely restored after the operation,
and the formation of chyme and the nutrition of the animal
may be carried on almost as perfectly as in health.

In thirty experiments on Mammalia, which M. Wern-
scheidt performed under Miiller’s direction, not the least
difference could be perceived in the action of narcotic
poisons introduced into the stomach, whether the pneu-
mogastric had been divided on both sides or not, provided
the animals were of the same species and size. It appears,
however, that such poisons as are capable of being
rendered inert by the action of the gastric fluid, may, if
taken into the stomach shortly after division of both
pneumogastric nerves, produce their poisonous effects ;
in consequence, apparently, of the temporary suspension
of the secretion of gastric fluid. Thus, in one of his
experiments, M. Bernard gave to each of two dogs, in one
of which he had divided the pneumogastric nerves, a
dose of emulsine, and half an hour afterwards a dose of
amygdaline, substances which are innocent alone, but
when mixed, produce hydrocyanic acid. The dog whose
nerves were cut, died in a quarter of an hour, the sub-

294 | DIGESTION.

stances being absorbed unaltered and mixing in the blood ;
in the other, the emulsine was decomposed by the gastric
fluid before the amygdaline was administered; therefore,
hydrocyanic acid was not formed in the blood, and the dog
survived.

The influence of the pneumogastric nerves over the

secretion of gastric fluid has been of late even more de-
cidedly shown by M. Bernard, who found that galvanic
stimulus of these nerves excited an active secretion of the
fluid, while a like stimulus applied to the sympathetic
nerves issuing, from the semilunar ganglia, caused a dimi-
nution and even complete arrest of the secretion.

The influence of the nervous system on the movements of the
stomach has been often seen in the retardation or arrest
of these movements after division of the pneumogastric
nerves. The results of irritating the same nerves were

ambiguous; but the experiments of Longet and Bischoff ’

have shown that the different results depended on whether
the stomach were digesting or not at the time of the experi-
ment. In the act of digestion, the nervous system of the
stomach appears to participate in the excitement which
‘prevails through the rest of its organization, and a stimulus
applied to the pneumogastric nerves is felt intensely, and
active movements of the muscular fibres of the stomach
follow; but in the inaction of fasting, the same stimulus
produces no effect. So, while the stomach is digesting,
the pylorus is too irritable to allow anything but chyme to
pass; but when digestion is ended, the undigested parts of
the food, and even large bodies, coins, and the like, may
pass through it.

Digestion of the Stomach after Death.

If an animal die during the process of gastric digestion,
and when, therefore, a quantity of gastric juice is present
in the interior of the stomach, the walls of this organ itself

=. -. 2

EE

POST-MORTEM DIGESTION. 295.

are frequently themselves acted on by their own secretion,
and to such an extent, that a perforation of considerable
size may be produced, and the contents of the stomach
may in part escape into the cavity of the abdomen.
This phenomenon is not unfrequently observed in post-
mortem examinations of the human body; but, as Dr.
Pavy observes, the effect may be rendered, by experi-
ment, more strikingly manifest. ‘‘If, for instance,”
he remarks, ‘‘an animal, as a rabbit, be killed at a
period of digestion, and afterwards exposed to artificial
warmth to prevent its temperature from falling, not
only the stomach, but many of the surrounding parts
will be found to have been dissolved. With a rabbit
killed in the evening, and placed in a warm situation (100°
to’. 110° Fahr.) during the night, I have seen in the
morning, the stomach, diaphragm, part of the liver, and
lungs, and the intercostal muscles of the side upon which
the animal was laid all digested away, with the muscles
and skin of the neck and upper extremity on the same
side also in a semi-digested state.”

From these facts, it becomes an interesting question why,
during life, the stomach is free from liability to injury
from a secretion, which, after death, is capable of such
destructive effects? John Hunter, who particularly drew
attention to the phenomena of post-mortem digestion, ex-
plained the immunity from injury of the living stomach,
by referring it to the protective influence of the “ vital
principle.” But this dictum has been called in question by
subsequent observers. It is, indeed, rather a statement
of a fact, than an explanation of its cause. It must be
confessed, however, that no entirely satisfactory theory has
been yet stated as a substitute.

It is only necessary to refer to the idea of Bernard, that
the living stomach finds protection from its secretion in the
presence of epithelium and mucus, which are constantly
renewed in the same degree that they are constantly dis-

296° | DIGESTION.

solved, in order to remark that this theory has been
disproved by experiments of Pavy’s, in which the mucus
membrane of the stomachs of dogs was dissected off for a
small space, and, on killing the animals some days after-
wards, no sign of digestion of the stomach was visible.
‘‘Upon one occasion, after removing the mucous mem-
brane and exposing the muscular fibres over a space of
about an inch and a half in diameter, the animal was
allowed to live for ten days. It ate food every day, and
seemed scarcely affected by the operation. Life was des-
troyed whilst digestion was being carried on, and the lesion
in the stomach was found very nearly repaired : new matter
had been deposited in the place of what had been removed,
and the denuded spot had contracted to much less than
its original dimensions.”

Dr. Pavy believes that the natural alkilinity of the
blood, which circulates so freely during life in the walls of
the stomach, is sufficient to neutralize the acidity of the
gastric juice, were it, so to speak, to make an attempt at
digesting parts with which it has no business; and as may
be gathered from what has been previously said (p. 283),
the neutralization of the acidity of the gastric secretion is
quite sufficient to destroy its digestive powers. He also

very ingeniously argues that this very alkilinity must, from’

the conditions of the circulation naturally existing in the
walls of the stomach, be increased in proportion to the
need of its protective influence. ‘‘In the arrangement of
the vascular supply,’’ he remarks ‘‘a doubly effective
barrier is, as it were, provided. The vessels pass from
below upwards towards the surface: capillaries having
this direction _ramify between the tubules by which the
acid of the gastric juice is secreted; and being separated
by secretion below, must leave the blood that is proceeding
upwards correspondingly increased in alkilinity ; and thus,
at the period when the largest amount of acid is flowing
into the stomach, and the greatest protection is required,

ids

- ia
a ae

ee

ee le ae le

be

5 td Dear

DIGESTION IN THE INTESTINES. 207

then is the provision afforded in its highest state of
efficiency.”

Dr. Pavy’s theory is the best and most ingenious hitherto
framed in connection with this subject; but the experi-
ments adduced in its favour are open to many objections,
and afford only a negative support to the conclusions they
are intended to prove. The matter, therefore, can scarcely
be considered finally settled.

DIGESTION IN THE INTESTINES.

The intestinal canal is divided into two chief portions,
named, from their differences in diameter, the small and
large intestine. These are continuous with each other, and
communicate by means of an opening guarded by a valve,
the tleo-ce@cal valve, which allows the passage of the pro-
ducts of digestion from the small into the large bowel, but
not, under ordinary circumstances, in the opposite direction.

The structure and functions of each organ or tissue con-
cerned in intestinal digestion will be first described in
detail, and afterwards a summary will be given of the
changes which the food undergoes in its passage through
the intestines, Ist, from the pylorus to the ileo-ceecal valve ;
and, 2nd, from the ileo-ceecal valve to the anus.

Structure and Secretions of the Small Intestine.

The small intestine, the average length of which in an
[ sau is about twenty feet, has been divided, for conve-
nience of description, into three portions, viz., the duo-
denum, which extends for eight or ten inches beyond the
pylorus ; the jejunum, which occupies two-fifths, and the
dleum, which occupies three-fifths of the rest of the canal.
The small intestine, like the stomach, is constructed of
three principal coats, viz., the serous, muscular, and
mucous. ‘The serous coat, formed by the visceral layer of
the peritoneum, need not be here specially described. The
fibres of the muscular coat of the small intestine are ar-
ranged in two layers; those of the outer layer being

298 DIGESTION.

disposed longitudinally ; those of the inner layer trans-
versely, or in portions of circles encompassing the canal.
They are composed of the unstriped kind of muscular fibre.

Between the mucous and muscular coats, there is a layer
of submucous tissue, in which numerous blood-vessels and a
rich plexus of nerves and ganglia are imbedded (Meissner).

The mucous membrane is the most important coat in
relation to the function of
digestion. The following
structures which enter into
the composition may be
= now successively described ;
\ the valvule conniventes ;
7, the villi; and the glands.
24+ The general structure of the
" mucous membrane of the
intestines resembles that
of the stomach (p. 266),
and, like it, is lined on its
inner surface by columnar
epithelium. Lymphoid or Retiform tissue | (fig. 72) enters
largely into its construction; and on its deep surface is ‘a
layer of the muscularis mucos@ (p. 276) 26 {

Valvule Conniventes.

The valvuleze conniventes commence in the duodenum,
about one or two inches beyond the pylorus, and becoming
larger and more numerous immediately beyond the en-
trance of the bile-duct, continue thickly arranged and well
developed throughout the jejunum; then, gradually
diminishing in size and number, they cease near the

* Fig. 72. The figure represents a cross section of a small fragment of
the mucous membrane, including one entire crypt of Lieberkiihn and
parts of several others: a, cavity of the tubular glands or crypts ; 6, one
of the lining epithelial cells; ce, the lymphoid or retiform spaces, of
which some are empty, and others occupied by lymph cells, as at d,

a a ee, a

vw?

Nn a “aa

THE VALVULA CONNIVENTES. 299

middle of the ileum. In structure they are formed by a
doubling inwards of the mucous membrane, the crescentic,
nearly circular, folds thus formed being arranging trans- , ¢<_
versely with regard to the axis of the intestine, and each
individual fold seldom extending around more than 4 or 2
of the bowel’s circumference. Unlike the ruge in the
stomach, they do not disappear on distension. Only an
imperfect notion of their natural position and function can
be obtained by looking at them after the intestine has been
laid open in the usual manner. To understand them
aright, a piece of gut should be distended either with air
or alcohol, and not opened until the tissues have become
hardened. On then making a section, it may be seen that
instead of disappearing, as the rugee in the stomach would
under similar circumstances, they stand out at right angles
to the general surface of the mucous
membrane (fig. 73). Their functions
are probably these—Besides (1) offer-
ing a largely increased surface for
secretion and absorption, they proba- |
bly (2) prevent the too rapid passage
of the very liquid products of gastric
digestion, immediately after their es-
cape from the stomach, and (3), by
their projection, and consequent inter-
ference with an uniform and untrou-
bled current of the intestinal contents,
probably assist in the more perfect
mingling of the latter with the secre-
tions poured out to act on them.
Glands of the Small Intestine.—The glands are of three )
principal kinds, named after their describers, the glands of |
Lieberkiihn, of Peyer, and of Brunn. The glands or fol- {|

* Fig. 73. Piece of small intestine (previously distended and hardened
by alcohol) laid open to show the normal position of the valvule con-
niventes.

300 DIGESTION.

-

licles of Lieberkiihn are simple tubular depressions of
the intestinal mucous membrane, thickly distributed over

the whole surface both of the large and_small
We intestines. In the small intestine they are visible
Se only with the aid of a lens; and their orifices
appear as minute dots scattered between the villi.
They are larger in the large intestine, and
increase in size the nearer they approach the anal
end of the intestinal tube; and in the rectum their
orifices may be visible to the naked eye. In
length they vary from =}, to =1, of aline. Each
tubule (fig. 74) is constructed of the same essential
parts as the intestinal mucous membrane, viz.,
a fine structureless membrana propria, or base-
ment membrane, a layer of cylindrical epithelium
lining it and capillary blood-vessels covering its exterior.
Their contents appear to vary, even in health; the varieties
being dependent, probably, on the period of time in rela-
tion to digestion at which they are examined. At the
bottom of the follicle, the contents usually consist of a
granular material, in which a few cytoblasts or nuclei
are imbedded; these cytoblasts, as they ascend towards
the surface, are supposed to be gradually developed into
nucleated cells, some of which are discharged into the
intestinal cavity. The purpose served by the material
secreted by these glands is still doubtful. Their large
number and the extent of surface occupied by them, seem,
however, to indicate that they are concerned in other and
higher offices than the mere production of fluid to moisten
the surface of the mucous membrane, although, doubtless,
this is one of their functions.

The glands of Peyer occur exclusively in the small intes-
tine. They are found in greatest abundance in the lower
part of the ileum near to the ileo-czecal valve. They are

on bo O 0 Gayo tH
PA TAMMARAANSAINARAALA RRA R Ream Rag Bix
OE EOS OHNE A} 0 ho)o}ofofcyfololsf

* Fig. 74. A gland of Lieberkiihn,

wo .

—

ee ae ee ee

—— =

»
ives

o°*7 ms)

wats ae ee

PEYER’S GLANDS. 301

met with in two conditions, viz., either scattered singly, |
in which case they are termed glandul@ solitarie, or aggre- |
gated in groups varying from one to three inches in length
and about half-an-inch in width, chiefly of an oval form,
their long axis parallel with that of the intestine. In this |

placed almost always opposite the attachment of tho
mesentery. In structure, and probably in function, there
is no essential difference between the solitary glands and

Fig. 75.*

the individual bodies of which each group or patch is
made up; but the surface of the solitary glands (fig. 76) is |
beset with villi, from which those forming the agminate |
patches (fig. 77) are usually free. In the condition in |
which they have been most commonly examined, each
gland apppears as a circular opaque-white sacculus, from
half a line to a line in diameter, and, according to the
degree in which it is developed, either sunk beneath, or
more or less prominently raised on, the surface of a
depression or fossa in the mucous membrane. Each gland

* Fig. 75. Agminate follicles, or Peyer’s patch, in a state of disten-
sion : magnified about 5 diameters (after Boehm).

302 DIGESTION.

is surrounded by openings like those of Lieberkiihn’s —
follicles (see fig. 77) except that they are more elongated ;
and the direction of the long diameter of each opening is
such that the whole produce a radiated appearance around
the white sacculus. These openings appear to belong to
tubules identical with Lieberkiihn’s follicles: they have no
communication with the sacculus, and none of its contents
escape through them on pressure. Neither can any 5

! VF ee

e,
e
ee

"en.0 %
H_ i

gland itself (see fig. 78).

Each gland is an imperfectly closed sac or follicle formed
of a tolerably firm membranous capsule of fine connective
tissue, imbedded in a rich plexus of minute blood-vessels,
many fine branches from which pass through the capsule
and enter, chiefly loopwise, the interior of the follicle
(fig. 79). Entering into the formation of the sacculus,

\ permanent opening be detected in the sacculus or Peyer’s

ia eee ee a ae oe, ee Te

* Fig. 76. Solitary gland of small intestine (after Boehm).

+ Fig. 77. Part of a patch of the so-called Peyer’s glands magnified,
showing the various forms of the sacculi, with their zone of foramina.
The rest of the membrane marked with Lieberkiithn’s follicles, and
sprinkled with villi (after Boehm).

ey ee, ee

.

PEYER’S GLANDS. 303

moreover, and forming a stroma or supporting framework
throughout its interior, is lymphoid or adenoid tissue (fig. 72),
continuous with that which forms a great part of the mucous
membrane outside it. The contents of each sac consist of a
pale greyish opalescent pulp, formed of albuminous and fatty
matter, and a multitude of nucleated corpuscles of various
sizes, resembling exactly those found in lymphatic glands.

The real office of these Peyerian glands or follicles is still
unknown. It was formerly believed that each follicle was
a kind of secreting-cell, which, when its contents were
fully matured, formed a Fig. 78.*
communication with the
cavity of the intestine by
the absorption or bursting
of its own cell-wall, and
of the portion of mucous
membrane over it, and
thus discharged its secre-
tion into the intestinal
canal. A small shallow
cavity or space was thought
to remain, for a time, after
this absorption or dehi-
scence, but shortly to disappear, together with all trace of
the previous gland.

More recent acquaintance with the real structure of
these bodies seems, however, to prove that they are not
mere temporary gland-cells which thus discharge their
elaborated contents into the intestine and then disappear,
but that they are rather to be regarded as structures

* Fig. 78. Side-view of a portion of intestinal mucous‘membrane of
a cat, showing a Peyer’s gland (@) : it is imbedded in the submucous
tissue (f), the line of separation between which and the mucous mem-
brane passes across the gland: 6, one of the tubular follicles, the orifices
of which form the zone of openings around the gland : c, the fossa in
the mucous membrane : d, villi : ¢, follicles of Lieberkiihn (after Bendz).

304 DIGESTION.

analogous to lymphatic or absorbent glands, and that
| their office is to take up certain materials from the chyle,
elaborate and subsequently discharge them into the lacteals,
with which vessels they appear to be closely connected,
, although no direct communication has been proved to
exist between them.
Moreover, it has been lately suggested that since the
molecular and cellular contents of the glands are so
abundantly traversed by minute blood-vessels, important

Fig. 79.*
(a Pr:
<= =< 4, Nae TAVIN
SAh AN nm
qN \ tin,
NNN
PANS
—— “ae [67
(8: 4g e
ey KY Qf — —9
- p VA Rg
. A \. WW
Sees NS xe (

changes may mutually take place between these contents
and the blood in the vessels, material being abstracted
from the latter, elaborated by the cells, and then restored

* Fig. 79. Transverse section of injected Peyer’s glands (from K@6l-
liker). The drawing was taken from a preparation made by Frey: it

represents the fine capillary looped network spreading from the sur- —

rounding blood-vessels into the interior of three of Peyer’s capsules
from the intestine of the rabbit.

— ———

BRUNN’S GLANDS. 305

to the blood, much in the same manner as is believed to be
the case in the so-called vascular glands, such as the spleen,
thymus, and others;.and that thus Peyer’s glands should
also be regarded as closely analogous to these vascular
glands. Possibly they may combine the functions both of
lymphatic and vascular glands, absorbing and elaborating
material both from the chyle and from the blood within
their minute vessels, and transmitting part of the lacteal
system and part direct to the blood.

Fig. 80.*

Brunn’s glands (fig. 80) are confined to the duodenum ; },
they are most abundant and thickly set at the commence-
ment of this portion of the intestine, diminishing gradually
as the duodenum advances. Situated beneath the mucous |’
membrane, and imbedded in the submucous tissue, they
are minutely lobulated bodies, visible to the naked eye,
like detached small portions of pancreas, and provided with
permanent gland-ducts, which pass through the mucous
membrane and open on the internal surface of the intestine.

* Fig. 80. Enlarged view of one of Brunn’s glands from the human
duodenum (from Frey), The main duct is seen superiorly ; its branches
are elsewhere hidden by the bunches of opaque glandular vesicles.

x

306 DIGESTION.

As in structure, so probably in function, they resemble the
pancreas; or at least stand to it in a similar relation to
that which the small labial and buccal glands occupy in
relation to the larger salivary glands, the parotid and
submaxillary. . _

The Villi (figs. 81, 82) are confined exclusively to the
mucous membrane of the small intestine. They are minute
vascular processes, from a quarter of a line to a line and
two-thirds in length, covering the surface of the mucous
membrane, and giving it a peculiar velvety, fleecy appear-
ance. Krauss estimates them at fifty to ninety in number
in a square line, at the upper part of the small intestine,
and at forty to seventy in the same area at the lower part.
They vary in form even in the same animal, and differ
according as the lymphatic vessels they contain are empty
or full of chyle; being usually, in the former,case, flat
and pointed at their summits, in the latter cylindrical or
clavate. ;

Each villus consists of a small projection of mucous:
membrane, and its interior is therefore supported through-
out by fine retiform or adenoid tissue, which forms the
framework or stroma in which the other constituents are
contained. J

The surface of the villus is clothed by columnar epithe-
lium, which rests on a fine basement membrane; while
within this are found, reckoning from without inwards,
blood-vessels, fibres of the muscularis mucose, and a single
lymphatic, or lacteal vessel rarely looped or branched (fig.
81); besides granular matter, fat-globules, etc.

The epithelium is of the columnar kind, and continuous
with that lining the other parts of the mucous membrane.
The cells are arranged with their long axis radiating from
the surface of the villus (fig. $1), and their smaller ends
resting on the basement membrane. Some doubt exists
concerning the minute structure of these cells and their
relation to the deeper parts of the villus.

i a a

THE VILLI. 307

Beneath the basement or limiting membrane there is a
rich supply of blood-vessels. ‘Two or more minute arteries
are distributed within each villus; and from their capil-

Fig. 81.*

laries, which form a dense network, proceed one or two
small veins, which pass out at the base of the villus.

The layer of the muscularis mucose in the villus forms a
kind of thin hollow cone immediately around the central _
lacteal, and is, therefore, situate beneath the blood-vessels.
The addition of acetic acid to the villus brings out the
characteristic nuclei of the muscular fibres, and shows the
size and position of the layer most distinctly. Its use is

* Fig. 81. (Slightly altered from Teichmann.) a. Villus of sheep.
B. Villi of man.
x 2

308 DIGESTION.

still unknown, although it is impossible to resist the belief,
that it is instrumental in the propulsion of chyle along the
lacteal.

Fig. $2.*

wy,
ee”

The lacteal vessel enters the base of each villus, and pass-

* Fig. 82. (From Teichmann.) A, lacteals in villi. p, Peyer’s glands.
; and D, superficial and deep network of lacteals in submucous tissue.
L, Lieberkiihn’s glands. , small branch of lacteal vessel on its way to
mesenteric gland. H and 0, muscular fibres of intestine, 8s, peritoneum.

THE LARGE INTESTINE. 309

ing up in the middle of it, extends nearly to the tip, where
it ends commonly by a closed and somewhat dilated ex-
tremity. In the larger villi there may be two small lacteal
vessels which end by a loop (fig. 81), or the lacteals may
form a kind of network in the villus. The last method
of ending, however, is rarely or never seen in the human
subject, although common in some of the lower animals
(a, fig. 81).

The office of the villi is the absorption of chyle from the
completely digested food in the intestine. The mode in

ese

which they effect this will be considered in the chapter on

ABSORPTION.

Structure of the Large Intestine.

The large intestine, which in an adult is from about 4 to
6 feet long, is subdivided for descriptive purposes into three
portions, viz. :—The ca@cwm, a short wide pouch, commu-
nicating with the lower end of the small intestine through
an opening, guarded by the ileo-cecal valve; the colon,
continuous with the cecum, which forms the principal
part of the large intestine, and is divided into an ascend-
ing, transverse and descending portion; and the rectum,
which, after dilating at its lower part, again contracts,
and immediately afterwards opens externally through the
anus. Attached to the cecum is the small appendix
vermiformis.

Like the small intestine, the large is constructed of three
principal coats, viz., the serous, muscular, and mucous.
The serous coat need not be here particularly described.
Connected with it are the small processes of peritoneum
containing fat, called appendices epiploice. The fibres of
the muscular coat, like those of the small intestine, are
arranged in two layers—the outer longitudinally, the
inner circularly. In the cecum and colon, the longi-
tudinal fibres, besides being, as in the small intestine,
thinly disposed in all parts of the wall of the bowel, are

?
:
;

=

310 DIGESTION.

. collected, for'the most part, into three strong bands, which
being shorter, from end to end, than the other coats of
the intestine, hold the canal in folds, bounding inter-
mediate sacculi. On the division of these bands, the intes-
tine can be drawn out to its full length, and it then
assumes, of course, an uniformly cylindrical form. In the
rectum, the fasciculi of these longitudinal bands spread
out and mingle with the other longitudinal fibres, forming
with them a thicker layer of fibres than exists on any
other part of the intestinal canal. The circular muscular
fibres are spread over the whole surface of the bowel, but
are somewhat more marked in the intervals between the
sacculi. ‘Towards the lower end of the rectum they become
more numerous, and at the anus they form a strong band
called the internal sphincter muscle.

The mucous membrane of the large, like that of the
small intestine, is lined throughout by columnar epithe-
lium, but, unlike it, is quite smooth and destitute of villi,
and is not projected in the form of valvule conniventes.
Its general microscopic structure resembles that of the
small intestine.

Glands of the Large Intestine-—The glands with which
the large intestine is provided are of two kinds, the tubular
and lenticular.

The tubular glands, or glands of Lieberkiihn, resemble
those of the small intestine, but are somewhat larger
and more numerous. ‘They are also more uniformly
distributed.

The lenticular glands are most numerous in the cecum
and vermiform appendix. They resemble in shape and
structure, almost exactly, the solitary glands of the small
intestine, and, like them, have no opening. Just over
them, however, there is commonly a small depression in
the mucous membrane, which has led to the erroneous
belief that some of them open on the surface.

The functions discharged by the glands found in the

FO rag ttyl

THE ILEO-CZ/ECAL VALVE. 311

large intestine are not known with any certainty, but
there is no reason to doubt that they resemble very nearly
those discharged by the glands of like structure in the
small intestine.

The difficulty of determining the function of any single
set of the intestinal glands seems indeed almost insuper-
able, so many fluids being discharged together into the
intestine ; for all acting, probably, at once, produce a com-
bined effect upon the food, so that it is almost impossible
to discern the share of any one of them in digestion.

Ileo-cacal valve.—The ileo-ceecal valve is situate at the
place of junction of the small with the large intestine, and
guards against any reflux of the contents of the latter into
the ileum. Itis composed of two semilunar folds of mucous
membrane. Each fold is formed by a doubling inwards of
the mucous membrane, and is strengthened on the outside
by some of the circular muscular fibres of the intestine,
which are contained between the outer surfaces of the two
layers of which each fold is composed. .The inner surface
of the folds is smooth ; the mucous membrane of the ileum
being continvous with that of the cecum. That surface
of each fold which looks towards the small intestine is

covered with villi, while that which looks to the cecum |
has none. When the cecum is distended, the margins of —

the folds are stretched, and thus are brought into firm
apposition one with the other.

While the circular muscular fibres of the bowel at the
junction of the ileum with the cecum are contained
between the outer opposed surfaces of the folds of mucous
membrane which form the valve, the longitudinal mus-
cular fibres and the peritoneum of the small and large
intestine respectively are continuous with each other,
without dipping in to follow the circular fibres and the
mucous membrane. In this manner, therefore, the folding
inwards of these two last-named structures is preserved,
while on the other hand, by dividing the longitudinal

312 DIGESTION. '

muscular fibres and the peritoneum, the valve can be made
to disappear, just as.the constrictions between the sacculi
of the large intestine can be made to disappear by perform-
ing a similar operation.

The Pancreas, and its Secretion. 4

The pancreas is situated within the curve formed by the
duodenum; and its main duct opens into that part of the
intestine, either through a small opening or through a duct
common to itself and to the liver. The pancreas, in its
minute anatomy, closely resembles the salivary glands;
and the fluid elaborated by it appears almost identical with
saliva. When obtained pure, in all the different animals
in which it has*been hitherto examined, it has been found
colourless, transparent, and slightly viscid. It is alkaline
when fresh, and contains a peculiar animal matter named
pancreatin, and certain salts, both of which are very similar
to those found in saliva. In pancreatic secretion, however,
there is no sulpho-cyanogen. Pancreatin is a substance
coagulable by heat, and in many other respects very
like albumen: to it the peculiar digestive power of the
pancreatic secretion is probably due. Like saliva, the
pancreatic fluid, shortly after its escape, becomes neutral
and then acid.

The following is the mean of three analyses by

Schmidt :—
\

Composition of Pancreatic Secretion.
Water . : ‘ ! ; ; a: ; . 980°45
Solids ; - ¢ ; 3 : a ., o- SS
Pancreatin ‘ “ 4 ; . . E278
Inorganic bases and salts. , eres 6°84
19°55

The functions of the pancreas are probably as follows :—
I. Numerous experiments have shown, that starch is

—— a

THE PANCREATIC SECRETION. 313

acted upon by the pancreatic secretion, or by portions of
pancreas put in starch paste, in the same manner that it
is by saliva and portions of the salivary glands. And
although, as before stated (p. 262), many substances be-
sides those glands can excite the transformation of starch
into dextrin and grape-sugar, yet it appears probable
that the pancreatic fluid, exercising this power of trans-
formation, is largely subservient to the purpose of digesting
starch. MM. Bouchardat and Sandras have shown that
the raw starch-granules which have passed unchanged
through the crops and gizzards of granivorous birds, or
through the stomachs of herbivorous Mammalia, are, in
the small intestine, disorganized, eroded, and finally dis-
solved, as they are when exposed, in experiment, to the
action of the pancreatic fluid. The bile cannot effect such
a change in starch; and it is most probable that the pan-
creatic secretion is the principal agent in the transforma-
tion, though it is by no means clear that the office may
not be shared by the secretion of the intestinal mucous
membrane, which also seems to possess the power of con- —
verting starch into sugar.

2. The existence of a pancreas in Carnivora, which have
little or no starch in their food, and the results of various
observations and experiments, leave very ltttle doubt that
the pancreatic secretion also assists largely in the digestion
of fatty matters, by transforming them into a kind of
emulsion, and thus rendering them capable of absorption
by the lacteals. Several cases have been recorded in which
the pancreatic duct being obstructed, so that the secretion
could not be discharged, fatty or oily matter was abun-
dantly discharged from the intestines. In nearly all these
cases, indeed, the liver was coincidently diseased, and the
change or absence of the bile might appear to contribute
to the result; yet the frequency of extensive disease of
the liver, unaccompanied by fatty discharges from the
intestines, favours the view that, in these cases, it is to the
_ absence of the pancreatic fluid from the intestines that the

314 DIGESTION.

excretion or non-absorption of fatty matter should be
ascribed. In Bernard’s experiments too, fat always ap-
peared in the evacuations when the pancreas was destroyed
or its duct tied. Bernard, indeed, is of opinion that to
emulsify fat is the express office of the pancreas, and the
evidence that he and others have brought forward in sup-
port of this view is very weighty. The power of emulsify-
ing fat, however, although perhaps mainly exercised by
the secretion of the pancreas, is evidently possessed to
some extent by other secretions poured into the intestines,
and especially by the bile.

3. The pancreatic secretion discharges a third function
also, namely, that of dissolving albuminous substances ;
the peptone produced by the action of the pancreatic secre-
tion on proteids not differing essentially from that formed
by the action of the gastric juice (see p. 285).

Structure of the Liver.

The liver is an extremely vascular organ, and receives
its supply of blood from two distinct vessels, the portal
vein and hepatic artery, while the blood is returned from it
into the vena cava inferior by the hepatic vein. Its secre-
tion, the bile, is conveyed from it by the hepatic duct, either
directly into the intestine, or, when digestion is not going
on, into the cystic duct, and thence into the gall-bladder,
where it accumulates until required. The portal vein,
hepatic artery, and hepatic duct branch together throughout
the liver, while the hepatic vein and its tributaries run by
themselves.

On the outside the liver has an incomplete covering of
peritoneum, and beneath this is a very fine coat of areolar
tissue, continuous over the whole surface of the organ.
It is thickest where the peritoneum is absent, and is con-
tinuous on the general surface of the liver with the fine,
and, in the human subject, almost imperceptible, areolar
tissue investing the lobules. At the transverse fissure itis

— =. ~~ ™

STRUCTURE OF THE LIVER. 315

merged in the areolar investment called Glisson’s capsule,
Fig 33.* |

which, surrounding the portal vein, hepatic artery, and
hepatic duct, as they enter at
this part, accompanies them Fig. 84.
in their branchings through
the substance of the liver.
The liver is made up of
small roundish or oval por-
tions called lobules, each of
which is about 5, of an inch
in diameter, and composed of
the minutest branches of the portal vein, hepatic artery,
hepatic duct, and hepatic vein; while the interstices of

* Fig. 83. The liver has been turned over from left to right so as
to expose the lower surface. 1, left lobe; 2, 3, 4, 5, right lobe;
6, lobulus quadratus; 7, pons hepatis; 8, 9, 10, lobulus Spigelii ;
11, lobulus caudatus; 12, 13, transverse or portal fissure with the
great vessels; 14, hepatic.artery ; 15, vena porte; 16, anterior part
of the longitudinal fissure, containing 17, the round ligament or ob-
literated remains of the umbilical vein ; 18, posterior part of the same
fissure, containing 19, the obliterated ductus venosus; 20, 21, 22,
gall-bladder ; 23, cystic duct; 24, hepatic duct; 25, fossa containing

316 DIGESTION,

these vessels are filled by the liver cells. These cells
(fig. 84) which make up a great portion of the substance
of the organ, are rounded or polygonal from about <1, to
choo of an inch in diameter, containing well-marked nuclei
and granules, and having sometimes a yellowish tinge,
especially about their nuclei; frequently, they contain also
various sized particles of fat (fig. 84 8). Each lobule is
vary sparingly invested by areolar tissue.

Fig. 85.* To understand the
q . distribution of -the
blood-vessels in the
liver, it will be well
to trace, first, the two
blood-vessels and the
duct which enter the
organ on the under
surface at the trans-
verse fissure, viz., the
portal vein, hepatic
artery, and hepatic
duct. As before re-
marked, all three
run in company, and
their appearance on
longitudinal section
is shown in fig 85. Running together through the substance
of the liver, they are contained in small channels, called
portal canals, their immediate investment being a sheath
of areolar tissue, called Glisson’s capsule.

26, the vena cava inferior ; 27, opening of the capsular vein ; 28, small
part of the trunk of the right hepatic vein; 29, trunk of the left
hepatic vein ; 30, 31, openings of the right and left diaphragmatic veins.

* Fig. 85. Longitudinal section of a portal canal, containing a portal
vein, hepatic artery and hepatic duct, from the pig (after Kiernan) %. Pp,
branch of vena porte, situated in a portal canal, formed amongst the
lobules of the liver, and giving off vaginal branches; there are also
seen within the large portal vein numerous orifices of the smallest inter-
lobular veins arising directly from it ; a, hepatic artery ; d, hepatic duct.

STRUCTURE OF THE LIVER. 317

To take the distribution of the portal vein first :—In
its course through the liver this vessel gives off small
branches, which divide and subdivide between the lobules
surrounding them and limiting them, and from this cir-
cumstance called inter-lobular veins. From these small
vessels a dense capillary network is prolonged into the
substance of the lobule, and this network gradually gather-
ing itself up, so to speak, into larger vessels, converges
finally to a single small vein, occupying the centre of the
lobule, and hence called intra-lobular. This arrangement
is well seen in fig. 86, which represents a transverse sec-
tion of a lobule. The smaller branches of the portal vein
being closely surrounded by the lobules, give off directly

Fig. 86.*

Pr ee

2 Ren Gp
= y ; /
Kia. J
fa ¥
La‘ S
L f

i

aj
4
Y

Ls
>

s\

LA

j iA Sees
we) UN egy ces ere ges THY 8
. Py as “i th rt t t 3h hig
iin Le) LOAVES ISN SE) Sar;
\y Cus 44 PP aay, ‘
3

-
- “tnd

inter-lobular veins (see fig. 85); but here and there, espe-
cially where the hepatic artery and duct intervene, branches

* Fig. 86. Cross section of a lobule of the human liver, in which
the capillary network between the portal and hepatic veins has been fully
injected (from Sappey) “°. 1. Section of the cntra-lobular vein ; 2, its
smaller branches collecting blood from the capillary network ; 3, inter-
lobular branches of the vena porte with their smaller ramifications
- passing inwards towards the capillary network in the substance of the
lobule.

318 DIGESTION.

called vaginal first arise, and breaking up in the sheath are
subsequently distributed like the others around the lobules
and become inter-lobular. The larger trunks of the portal
vein being more separated from the lobules by a thicker
sheath of Glisson’s capsule, give off vaginal branches
alone, which, however, after breaking up in the sheath,
are distributed like the others between the lobules, and
become inter-lobular veins.

The small intra-lobular veins discharge their contents into
veins called sub-lobular (fig. 88), while these again, by their

Fig. 87.*

BY YY

WY if
LY
Hy
Vk NX:

-
Ly
Up
“py
og Urh

* Fig. 87. Section of a portion of liver passing longitudinally
through a considerable hepatic vein, from the pig (after Kiernan) §. H,
hepatic venous trunk, against which the sides of the lobules (2) are
applied ; h, h, h, sublobular hepatic veins, on which the bases of the

lobules rest, and through the coats of which they are seen as polygonal

figures ; 7, mouth of the intralobular veins, opening into the sublobular
veins ; 7’, intralobular veins shown passing up the centre of some divided
lobules ; 7, 1, cut surface of the liver; ¢, c, walls of the hepatic venous
canal, formed by the polygonal bases of the lobules.

2 at oh wivjwa es

_STRUCTURE OF THE LIVER. 319

union, form the main branches of the hepatic vein, which
leaves the posterior border of
the liver to end by two or
three principal trunks in the
inferior vena cava, just before
its passage through the dia-
phragm. The sub-lobular and
hepatic veins, unlike the portal
- vein and its companions, have
little or no areolar tissue
around them, and their coats
being very thin, they form
little more than mere chan-
nels in the liver substance
which closely surrounds them.

The manner in which the lobules are connected with
the sublobular veins by means of the small intralobular veins
is well seen in the diagram, fig. 88 and in fig. 87, which
represent the parts as seen in a longitudinal section. The
appearance has been likened to a twig having leaves with-
out footstalks—the lobules representing the leaves, and
the sublobular vein the small branch from which it springs..
On a transverse section, the appearance of the intra-
lobular veins is that of 1, fig. 86, while both a transverse
and longitudinal section are exhibited in fig. 809.

The hepatic artery, the function of which is to distribute
blood for nutrition to Glisson’s capsule, the walls of the
ducts and blood-vessels, and other parts of the liver, is
distributed in a very similar manner to the portal vein, its
_blood being returned by small branches either into the
ramifications of the portal vein, or into the capillary plexus.
of the lobules which connects the inter- and intra-lobular
veins.

* Fig. 88. Diagram showing the manner in which the lobules of the
liver rest on the sublobular veins (after Kiernan).

320 DIGESTION.

The hepatic duct divides and subdivides in a manner
very like that of the portal vein and hepatic artery, the
larger branches being lined by cylindrical, and the smaller

Fig. 89.*

=
=
oy
SS

by small polygonal epithelium. The exact arrangement of
its terminal branches, however, and their relatoin to the
liver-cells have not been clearly made out, or, at least, have
not been agreed upon by different observers. The chief
theories on the subject are three in number :—

1. That the terminal branches of the hepatic duct form
an interlobular network, which abuts on the outermost
cells of a lobule, but does not enter the inside of the
lobule, or only for a little way.

2. That minute branches begin in the lobules between
the cells, not enclosing them.

3. That the ultimate branches begin in the lobules and
enclose hepatic cells.

* Fig. 89. Capillary network of the lobules of the rabbit’s liver
(from Kolliker), *. The figure is taken from a very successful injee-
tion of the hepatic veins, made by Harting : it shows nearly the whole
of two lobules, and parts of three others ; p, portal branches running in
the interlobular spaces ; , hepatic veins penetrating and radiating from
the centre of the lobules.

STRUCTURE OF THE LIVER. 325

The illustrations below will show the conflicting theories
at a glance.

* Fig. 90. Diagrams showing th the arrangement of the radicles of the
hepatic duct, according to different observers.

I. d, d, are two branches of the hepatic duct, which is supposed
to commence in a plexus situated towards the circumference of the
lobule marked 6, 6, called by Kiernan the biliary plexus. Within this
is seen the central part of the lobule, containing branches of the intra-
lobular vein.

2, A small fragment of an hepatic lobule, of which the smallest
intercellular biliary ducts were filled with colouring matter during
life, highly magnified (from Chrzonszczewsky ).

3. View of some of the smallest biliary ducts illustrating Beale’s
view of their relation to the biliary cells (from Kolliker after Beale),*+°._

The drawing is taken from an injected preparation of the pig’s liver ;
Y

322 DIGESTION.

Functions of the Liver.

The Secretion of Bile is the most obvious, and one of the-
chief functions which the liver has to perform; but, as,

will be presently shown, it is not the only one; for im-

portant changes are effected in certain constituents of the
blood in its transit through this gland, whereby they are
rendered more fit for their subsequent purposes in the-
animal economy.

The Bile.

Composition of the Bile-—The bile is a somewhat viscid.
fluid, of a yellow or greenish-yellow colour, a strongly
bitter taste, and when fresh with a scarcely perceptible:
odour; it has a neutral or slightly alkaline reaction, and
its specific gravity is about 1020., Its colour and degree

of consistence vary much, apparently independent of

disease ; but, as a rule, it- becomes gradually more deeply
coloured and thicker as it advances along its ducts, or
when it remains long in the gall-bladder, wherein, at
the same time, it becomes more viscid and ropy, of a
darker colour, and more bitter taste, mainly from its.
greater degree of concentration, on account of partial
absorption of its water, but partly also from being mixed.
with mucus. .
The following analysis is by Frerichs :—

Composition of Human Bile.

Water ; . ‘ ; , . ; . 859°2
Solids . : ; . ; : ; i AOS
1,000°0

a, small branch of an interlobular hepatic duct; 0, smallest biliary
ducts ; ¢, portions of the cellular part of the lobule in which the cells
are seen within tubes which communicate with the finest ducts.

—— oe Te a ——

THE BILE. 323

Big aes aie Fo
Fat or; , : ' 7 aes 6 9°2
Cholesterin : ; : ; ; 2°6
Mucus and colouring matters . renee 29°8
Salts . ! ; ; , ‘ ; yay

140°8

The Bilin or biliary matter when freed by ether from the
fat with which it is combined, is a resinoid substance, solu-
ble in water, alcohol, and alkaline solutions, and giving to
the watery solution the taste and general character of bile:
It is a compound of soda, with two resinous acids, named
glycocholic and taurocholic acids. The former consists of
cholic acid conjugated with glycin (or sugar of gelatin), the
latter of the same acid conjugated with taurin.

Fatty substances are found in variable proportions. Be-
sides the ordinary saponifiable fats, there is a small quantity
of cholesterin (p. 11), which, with the other free fats, is
probably held in solution by the tauro-cholate of soda.

A peculiar substance, which Dr. Flint has discovered in
the feces, and named stercorin (p. 342), is closely allied
to cholesterin; and Dr. Flint Fig. 91.*
believes that while one great
function of the liver is to ex-
crete cholesterin from the
blood, as the kidney excretes
urea, the stercorin of feeces
is the modified form in which
cholesterin finally leaves the
body. Ten grains and a half
of stercorin, he reckons, are
excreted daily.

The colowring matter of the bile has not yet been obtained
pure, owing to the facility with which it is decomposed.
it occasionally deposits itself in the gall-bladder as a

* Fig. 91. Crystalline scales of cholesterin,
¥ 2

324 DIGESTION.

yellow substance mixed with mucus, and in this state has
been frequently examined. It is composed of two colour-
ing matters, called biliverdin and bilifulvin. By oxidising
agencies, as exposure to the air, or the addition of nitric
acid, it assumes a dark green colour. In cases of biliary
obstruction, it is often re-absorbed, circulates with the blood,
and gives to the tissues the yellow tint characteristic of
jaundice.

There seems to be some relationship between the colour-
matters of the blood and bile, and, it may be added, be-
tween these and that of the urine also, so that it is possible
they may be, all of them, varieties of the same pigment,
or derived from the same source. Nothing, however, is at
present certainly known regarding the relation in which
one of them stands to the other. —

The mucus in bile is derived chiefly from the mucous
membrane of the gall-bladder, but in part also from the
hepatic ducts and their branches. It constitutes the residue
after bile is treated with alcohol. The epithelium with
which it is mixed may be detected in the bile with the
microscope in the form of cylindrical cells, either scattered
or still held together in layers. To the presénce of this
mucus is probably to be ascribed the rapid decomposition
undergone by the bilin ; fer, according to Berzelius, if the
mucus be separated, bile will remain unchanged for many
days.

The saline or inorganic constituents of the bile are similar
to those found in most other secreted fluids. It is possible
that the carbonate and neutral phosphate of sodium and
potassium, found in the ashes of bile, are formed in the
incineration, and do not exist as such in the fluid. Oxide
of iron is said to be a common constituent of the ashes of
bile, and copper is generally found in healthy bile, and
constantly in biliary calculi.

Such are the principal chemical constituents of bile ; but

THE BILE. 325

its physiology is, perhaps, better illustrated by its ultimate
elementary composition. According to Liebig’s analysis,
the biliary matter,—consisting of bilin and the products of
its spontaneous decomposition—yields, on analysis, 76 atoms
of carbon, 66 of hydrogen, 22 of oxygen, 2 of nitrogen,
and a certain quantity of sulphur.* Comparing this with
the ultimate composition of the organic parts of blood,
which may be stated at C,,H,,N,O,, with sulphur and
phosphorus—it is evident that bile contains a large pre-
ponderance of carbon and hydrogen, and a deficiency of
nitrogen. The import of this will presently appear.

Txsts ror Brrzx.—A common test for the presence of
bile consists of the addition of a small quantity of nitric
acid, when, if bile be present, a play of colours is produced,
beginning with green and passing through various tints |
to red. This test will detect only the colouring matter of -
the bile. :

The best test for the bilin is Pettenkofer’s. To the liquid)’
suspected to contain bile must be added, first, a drop or two
of a strong solution of cane-sugar (one part of sugar to
four parts of water), and immediately afterwards sulphuric \
acid, to the extent of about two-thirds of the liquid. On
first adding the acid, a whitish precipitate falls; but this
redissolves with a slight excess of the acid, and on the
further addition of the latter there appears a bright cherry-
red colour, gradually changing through a lake tint, to a dark
purple.

The process of secreting bile is probably continually going
on, but appears to be retarded during fasting, and accele-
rated on taking food. This was shown by Blondlot, who,

* The sulphur is combined with the taurin—one of the substances
yielded by the decomposition of bilin. According to Dr. Kemp, the
sulphur in the bile of the ox, dried and freed from mucus, colouring
matter, and salts, constitutes about 3 per cent.

/ /

326 DIGESTION.

having tied the common bile-duct of a dog, and established
a fistulous opening between the skin and gall-bladder,
whereby all the bile secreted was discharged at the surface,
noticed that when the animal was fasting, sometimes not
a drop of bile was discharged for several hours; but
that, in about ten minutes after the introduction of food
into the stomach, the bile began to flow abundantly, and
continued to do so during the whole period of digestion.
Bidder and Schmidt’s observations are quite in accordance
with this.

The bile is probably formed first in the hepatic cells;
then, being discharged into the minute hepatic ducts, it
passes into the larger trunks, and from the main hepatic
duct may be carried at once into the duodenum. But,
probably, this happens only while digestion is going on ;
during fasting it flows from the common bile-duct into
the cystic duct, and thence into the gall-bladder, where it
accumulates till, in the next period of digestion, it is dis-
charged into the intestine. The gall-bladder thus fulfils
what appears to be its chief or only office, that of a reser-
voir; for its presence enables bile to be constantly secreted
for the purification of the blood, yet insures that it shall all
be employed in the service of digestion, although digestion
is periodic, and the secretion of bile constant.

The mechanism by which the bile passes into the gall-
bladder is simple. The orifice through which the common
bile-duct communicates with the duodenum is narrower
than the duct, and appears to be closed, except when there
is sufficient pressure behind to force the bile through it.
The pressure exercised upon the bile secreted during the
intervals of digestion appears insufficient to overcome the
force with which the orifice of the duct is closed; and the
bile in the common duct, finding no exit in the intestine,
traverses the cystic duct, and so passes into the gall-bladder,
being probably aided in this retrograde course by the peri-
staltic action of the ducts. The bile is discharged from the

«% = ee hl

“— SoytT

—

THE BILE: MECONIUM. 327

gall-bladder, and enters the duodenum on the introduction

-of food into the small intestine: being pressed on by the
contraction of the coats of the gall-bladder, and probably
-of the common bile-duct also ; for both these organs contain

organic muscular fibre-cells. Their contraction is excited
by the stimulus of the food in the duodenum acting so as to
produce a reflex movement, the force of which is sufficient
to open the orifice of the common bile-duct.

Various estimates have been made of the quantity of bile

-discharged in the intestines in twenty-four hours: the
-quantity doubtless varying, like that of the gastric fluid, in

proportion to the amount of food taken. A fair average

-of several computations would give thirty to forty ounces

as the quantity daily secreted by man.
The purposes served by the secretion of bile may be con-

‘sidered to be of two principal kinds, viz., excrementitious
-and digestive.

As an excrementitious substance, the bile serves especi-

| ally as a medium for the separation of excess of carbon and

hydrogen from the blood; and its adaptation to this pur-
pose is well illustrated by the peculiarities attending its
secretion and disposal in the foetus. During intra-uterine
life, the lungs and the intestinal canal are almost inactive;
there is no respiration of open air or digestion of food ;
these are unnecessary, because of the supply of well-elabo-

-rated nutriment received by the vessels of the foetus at the

placenta. The liver, during the same time, is proportionally
Jarger than it is after birth, and the secretion of bile is
active, although there is no food in the intestinal canal upon
which it can exercise any digestive property. At birth, the

‘intestinal canal is full of thick bile, mixed with intestinal

‘secretion; for the meconium, or feeces of the foetus, are

-shown by the analyses of Simon and of Frerichs to contain

-all the essential principles of bile.

OR er elt

328 DIGESTION.

Composition of Meconium (Frerichs) :

Biliary resin. ; : : ; ei BRID

Common fat and Sealactaen : : Ay 5

Epithelium, mucus, pigment, and salts ; o S69"
100

In the foetus, therefore, the main purpose of the secretion
of bile must be the purification of the blood by direct
excretion, i.e., by separation from the blood, and ejection
from the body without further change. Probably all the
bile secreted in foctal life is incorporated in the meconium,
and with it discharged, and thus the liver may be said to
discharge a function in some sense vicarious of that of the
lungs. For, in the foetus, nearly all the blood coming from.
the placenta passes through the liver, previous to its dis-
tribution to the several organs of the body; and the
abstraction of carbon, hydrogen, and other elements of bile-
will purify it, as in extra-uterine life it is purified by the
separation of carbonic acid and water at the lungs.

The evident disposal of the footal bile by excretion, makes
it highly probable that the bile in extra-uterine life is.
also, at least in part, destined to be discharged as.
excrementitious. But the analysis of the feeces of both
children and adults shows that (except when rapidly dis-
charged in purgation) they contain very little of the bile
secreted, probably not more than one-sixteenth part of its
weight, and that this portion includes only its colouring,
and some of its fatty matters, but none of its essential
principle, the bilin. All the bilin is again absorbed from
the intestines into the blood. But the elementary compo-
sition of bilin (see p. 325) shows such a preponderance of
carbon and hydrogen, that it cannot be appropriated to
the nutrition of the tissues; therefore, it may be presumed
that after absorption, the carbon and hydrogen of the
bilin combining with oxygen, are excreted as carbonic:
acid and water. The destination of the bile is, on this.

ee) =a tae an ? os

THE BILE. 329

theory, essentially the same in both footal and extra-
uterine life; only, in the former, it is directly excreted, in
the latter for the most part indirectly, being, before final
ejection, modified in its absorption from the intestines, and
mingled with the blood.

The change from the direct to the indirect mode of
excretion of the bile may, with much probability, be con-
nected with a purpose in relation to the development of
heat. The temperature of the foctus is maintained by that
of the parent, and needs no source of heat within the
body of the foetus itself; but, in extra-uterine life, there is
(as one may say) a waste of material for heat when any
excretion is discharged unoxidized; the carbon and hydro-
gen of the bilin, therefore, instead of being ejected in the
feeces, are re-absorbed, in order that they may be combined
with oxygen, and that, in the combination, heat may be
generated.

_ From the peculiar manner in which the liver is supplied
with much of the blood that flows through it, it is probable,
as Dr. Budd suggests, that this organ is excretory, not
only for such hydro-carbonaceous matters as may need
expulsion from any portion of the blood, but that it serves
for the direct purification of the stream which, arriving by
the portal vein, has just gathered up various substances
in its course through the digestive organs—substances
which may need to be expelled; almost immediately after
their absorption. For it is easily conceivable that many
things may be taken up during digestion, which not only
are unfit for purposes of nutrition, but- which would be
positively injurious if allowed to mingle with the general
mass of the blood. The liver, therefore, may be supposed
placed in the only road by which such matters can pass
into the general current, jealously to guard against their
further progress, and turn them back again into an
excretory channel. The frequency with which metallic
poisons are either excreted by the liver or intercepted and

330 DIGESTION.

retained, often for a considerable time, in its own substance,
may be adduced as evidence for the probable truth of this
supposition.

Though one chief purpose of the secretion of bile may
thus appear to be the purification of the blood by ultimate
excretion, yet there are many reasons for believing that,
while it is in the intestines, it performs an important part in
the process of digestion. In nearly all animals, for example,
the bile is discharged, not through an excretory duct
communicating with the external surface or with a simple
reservoir, as most secretions are, but is made to pass into
the intestinal canal, so as to be mingled with the chyme
directly after it leaves the stomach; an arrangement, the
constancy of which clearly indicates that the bile has some
important relations to the food with which it is thus mixed.
A similar indication is furnished also by the fact that the
secretion of bile is most active, and the quantity discharged
into the intestines much greater, during digestion than at
any other time; although, without doubt, this activity of
secretion during digestion may, however, be in part
ascribed to the fact that a greater quantity of blood is sent
through the portal vein to the liver at this time, and that
this blood contains some of the materials of the food
absorbed from the stomach and intestines, which may need
to be excreted, either temporarily, to be re-absorbed, or
permanently.

Respecting the functions discharged by the bile in
digestion, there is little doubt that it assists in emulsifying
the fatty portions of the food, and thus rendering them
capable of being absorbed by the lacteals. . For it has
appeared in some experiments in which the common bile-
duct was tied, that although the process of digestion in the
stomach was unaffected, chyle was no longer well-formed ;
the contents of the lacteals consisting of clear, colourless
fluid, instead of being opaque and white, as they ordinarily
are, after feeding. (2.) It is probable, also, from the

FUNCTIONS OF THE LIVER. 331

result of some experiments by Wistinghausen and Hoff-
mann, that the moistening of the mucous membrane of the
intestines by bile may facilitate absorption of fatty matters

through it. |

(3.) The bile, like the gastric fluid, has a strongly
antiseptic power, and may serve to prevent the decompo-
sition of food during the time of its.sojourn in the intes-
tines. Theexperiments of Tiedemann and Gmelin show
that the contents of the intestines are much more foetid
after the common bile-duct has been tied than at other
times ; and the experiments of Bidder and Schmidt on
animals with an artificial biliary fistula, confirm this
observation ; moreover, itis found that the mixture of bile
with a fermenting fluid stops or spoils the process of fer-
mentation.

(4.) The bile has also been considered to act as a kind
of natural purgative, by promoting an increased secretion
of the intestinal glands, and by stimulating the intestines
to the propulsion of their contents. This view receives
support from ‘the constipation which ordinarily exists in
jaundice, from the diarrhoea which accompanies excessive
secretion of bile, and from the purgative properties of
ox-gall.

Nothing is known with certainty respecting the changes
which the re-absorbed portions of the bile undergo, either
in the intestines or in the absorbent vessels. That they
are much changed appears from the impossibility of
detecting them in the blood; and that part of this change
is effected in the liver is probable from an experiment
of Magendie, who found that when he injected bile
into the portal vein a dog was unharmed, but was
killed when he injected the bile into one of the systemic
vessels.

The secretion of bile, as already observed, is only one
of the purposes fulfilled by the liver. Another very im-
portant function appears to be that of so acting upon

332 DIGESTION.

certain constituents of the blood passing through it, as to:
render some of them capable of assimilation with the
blood: generally, and to prepare others for being duly

eliminated in the process of respiration. From the labours.

of M. Bernard, to whom we owe most of what we know

on this subject, it appears that the low form of albuminous.

matter, or albuminose, conveyed from the alimentary
canal by the blood of the portal vein, requires to be sub-

mitted to the influence of the liver before it can be

assimilated by the blood; for if such albuminous matter is
injected into the jugular vein, it speedily appears in the

urine; but if introduced into the portal vein, and thus.

allowed to traverse the liver, it is no longer ejected as a
foreign substance, but is probably incorporated with the
albuminous part of the blood.

An important influence seems also to be exerted by the
liver upon the saccharine matters derived from the alimen-
tary canal. The chief purpose of the saccharine and
amylaceous principles of food is, probably, in relation to
respiration and the production of animal heat; but in

order that they may fulfil this, their main office, it seems.

to be essential that they should undergo some intermediate
change, which is effected in the liver, and which consists

in their conversion into a peculiar form of saccharine

matter, very similar to glucose, or diabetic sugar. That
such influence is exerted by the liver seems proved by the
fact that when cane sugar is injected into the jugular vein

it is speedily thrown out of the system, and appears in the
urine; but when injected into the portal vein, and thus.

enabled to traverse the liver, it ceases to be excreted at the
kidneys ; and, what is still more to the point, a very large
quantity of glucose may be injected into the venous system

without any trace of it appearing in the urine. ' So that it.

may be concluded, that the saccharine principles of the

food undergo, in their passage through the liver, some

transformation necessary to the subsequent purpose they

——— a

ee bh fe ee

FORMATION OF SUGAR IN THE LIVER. 333

have to fulfil in relation to the respiratory process, and
without which, such purpose probably could not be pro-
perly accomplished, and the substances themselves would
be eliminated as foreign matters by the kidneys.

Then, again, it was discovered by Bernard, and the
discovery has been amply confirmed, that the liver pos-
sesses the remarkable property of forming glucose or grape-
sugar (C,H,,0,), or a substance readily convertible into
sugar, even out of principles in the blood which contain no
trace of saccharine or amylaceous matter. In Herbivora
and in animals living on mixed diet, a large part of the
sugar is derived from the saccharine and amylaceous
principles introduced in their food. But in animals fed
exclusively on flesh, and deprived therefore of this source
of sugar, the liver furnishes the means whereby it may be
obtained. Not only in Carnivora, however, but apparently
in all classes of animals, the liver is continually engaged,
during health, in forming sugar, or a substance closely
allied to it, in large amount. This substance may always
be found in the liver, even when absent from all other parts
of the body.

To demonstrate the presence of sugar in the liver, a por- /
tion of this organ, after being cut into small pieces, a
bruised in a mortar to a pulp with a small quantity of;
water, and the pulp is boiled with sulphate of soda in order
to precipitate albuminous and colouring matters. The de-
coction is then filtered and_may be tested for glucose. The
most usual test is Trommer’s, To the filtered solution an
equal quantity of liquor potassee is added, with a few drops
of a solution of sulphate of copper. The mixture is then
boiled, when the presence of sugar is indicated by a reddish-
brown precipitate of the suboxide of copper.

The researches of Bernard and others, however, have
shown that the sugar is not formed at once at the liver,
but that this organ has the power of producing a peculiar
substance allied to starch, which is readily convertible into

334 DIGESTION.

glucose when in contact with any animal ferment. This
substance has received the different names of slycogen,
glycogenic coma aye starch, hepatin.

Glycogen (C,,H,,O,,) is obtained by taking a portion
of liver from a recently killed animal, and, after cutting it

into small pieces, placing it for a short time in boiling

water. It is then bruised in a mortar, until it forms a
pulpy mass, and subsequently boiled in distilled water for
about a quarter of an hour.. The glycogen is precipitated
from the filtered decoction by the addition of alcohol.

When purified, glycogen is a white, amorphous, starch-
like substance, odourless and tasteless, soluble in water,
but insoluble in alcohol. It is converted into glucose by
boiling with dilute acids, or by contact with any animal
ferment.

There are two chief theories concerning the immediate
destination of glycogen. (1.) According to Bernard and
most other physiologists, its conversion into sugar takes
place rapidly during life, and the sugar is conveyed away
by the blood of the hepatic veins to be consumed in
respiration at the lungs. (2.) Pavy and others believe that
the conversion into sugar only occurs after death, and that
during life no sugar exists in healthy livers,—the amyloid
substance or glycogen being prevented by some force from
undergoing the transformation. The chief arguments
advanced by Pavy in support of this view are, first, that
scarcely a trace of sugar is found in blood drawn during
life from the right ventricle, or in blood collected from the

right side of the heart immediately after an animal has -

been suddenly deprived of life, while if the examination be
delayed for a little while after death, sugar in abundance
may be found in such blood; secondly, that the liver,
like the venous blood in the heart, is, at the moment of
death, almost completely free from sugar, although after-
wards its tissue speedily becomes saccharine, unless the
formation of sugar be prevented by freezing, boiling, or

= ~~

FORMATION OF SUGAR IN THE LIVER. 335

other means calculated to interfere with the action of a
ferment on the amyloid substance of the organ. Instead
of adopting Bernard’s view, that normally, during life,
glycogen passes as sugar into the hepatic venous blood, and
thereby is conveyed to the lungs to be further disposed of,
Pavy inclines to believe that it may represent an interme-
diate stage in the formation of fat from materials absorbed
from the alimentary canal.

_For the present we must remain uncertain as to which
of these theories contains most truth in it.

Whatever be the destination of this peculiar amyloid
substance formed at the liver, most recent observers agree
that it is formed at, and exists within, the hepatic cells,
from which it may be extracted by the process just de-
scribed.

Much doubt exists also respecting the mode in which
glycogen is formed in the liver, and the materials
which furnish its source. Since its quantity is increased
after feeding, especially on substances containing much
sugar or starch, it is probable that part of it is derived
from saccharire principles absorbed from the digestive
canal; but since its formation continues even when there
is no starch or sugar in the food, the albuminous or fatty
principles also have been thought capable. of furnish-
ing part of it. Numerous experiments, however, having
proved that the liver continues to form sugar in animals
after prolonged starvation, and during hybernation, and
even after death, its production is clearly independent
of the elements of food. One of Bernard’s experiments
may be quoted in proof of this :—Having fed a healthy dog
for many days exclusively on flesh, he killed it, removed
the liver at once, and before the contained blood could
have coagulated, he thoroughly washed out its tissue by
passing a stream of cold water through the portal vein.
He continued the injection until the liver was completely

exsanguined, until the issuing water contained not a trace

336 | DIGESTION.

of sugar or albumen, and until no sugar was yielded by

portions of the organ cut into slices and boiled in water. .

Having thus deprived the liver of all saccharine matter,
he left it for twenty-four hours, and on then examining it,
found in its tissue a large quantity of soluble sugar, which
must clearly have been formed subsequently to the organ

being washed, and out of some previously insoluble and

non-saccharine substance. This and other experiments
led him and others to the conclusion that the formation
of the amyloid substance by the liver is the result of a
kind of secretion or elaboration out of materials in the
solid tissues of the gland—such secretion being probably
effected by the hepatic cells, in which, indeed, as pie’
observed, the substance has been detected.

According to this view, then, the liver may be regarded
as an organ engaged in forming two kinds of secretion,
namely, bile and sugar, or rather, glycogen readily con-
vertible into sugar. The former, chiefly excrementitious,
passes along the bile-ducts into the intestines, where it
may subserve some purposes in relation to digestion, and
is then for the most part re-absorbed, and ultimately
eliminated during the processes concerned in the produc-
tion of animal heat. The latter, namely sugar, being
soluble, is, unless Pavy’s view be correct, taken up by the
blood in the hepatic vein, conveyed. through the right side
of the heart to the lungs, where it is probably consumed in
the respiratory process, and thus contributes to the ses
duction of animal heat.

The formation of glycogen or of sugar is, like all other
processes in the living body, under the control of the
nervous system. Bernard discovered that by pricking the
floor of the fourth ventricle, the quantity of sugar formed
was so much in excess of the normal quantity, as to be ex-
creted by the kidney, and thus produce the leading symptom
of diabetes. Section of the inferior cervical ganglion of the
sympathetic nerve also produces diabetes.

:
. é .
—_= Po Bod

‘ ee Oe

cy SE antigen

¥

DIGESTION IN SMALL INTESTINE. 337

The channel by which the influence of the nervous

‘system is conducted in the preceding and similar experiments

is not accurately known; no theory having been perma-
nently established, which explains all the facts hitherto
observed in connection with the influence of the nervous
system on the production of glucose.

Summary of the Changes which take place in the Food during

its Passage through the Small Intestine.

In order to understand the changes in the food which
occur during its passage through the small intestine, it
will be well to refer briefly to the state in which it leaves

the stomach through the pylorus. It has been said

before, that the chief office of the stomach is not only to
mix into an uniform mass all the varieties of food that
reach it through the cesophagus, but especially to dissolve
the nitrogenous portion by means of the gastric juice.
The fatty matters, during their sojourn in the stomach,
become more thoroughly mingled with the other consti-
tuents of the fvod taken, but are not yet in a state fit for
absorption. The conversion of starch into sugar, which
began in the mouth, has been interfered with, although
not stopped altogether. The soluble matters—both those
which were so from the first, as sugar and saline matter,
and those which have been made so by the action of the
saliva and gastric juice—have begun to disappear by ab-
sorption into the blood-vessels, and the same thing has
befallen such fluids as may have been swallowed,—wine,
water, etc.

The thin pultaceous chyme, therefore, which, during the
whole period of gastric digestion, is being constantly
squeezed or strained through the pyloric orifice into the
duodenum, consists of albuminous matter, broken down,
dissolving and half dissolved, fatty matter, broken down,
but not dissolved at all, starch very slowly in process of

; Z

338 DIGESTION,

conversion into sugar, and as it becomes sugar, also dis-
solving in the fluids with which it is mixed; while with
these are mingled gastric fluid, and fluid that has been
swallowed, together with such portions of the food as are
not digestible, and will be finally expelled as part of the
feeces, |

On the entrance of the chyme into the duodenum, it is
subjected to the influence of the fluid secreted by Lieber-
kiihn’s and Brunn’s glands, before described, and to that
of the bile and pancreatic juice, which are poured into this
part of the intestine.

Without doubt, that part of digestion which it is a chief
duty of the small intestine to perform, is the alteration of
the fat in such a manner as to make it fit for absorption.
And there is no doubt that this change is chiefly effected
in the upper part of the small intestine. What is the

- exact share of the process, however, allotted respectively

|
|
|

to the bile, pancreatic secretion, and the secretion of the
intestinal glands, is still uncertain. It is most probable,
however, that the pancreatic secretion and the bile are
the main agents in emulsifying the fat, and that they do:
this by direct admixture with it. They also promote its.
absorption by moistening the surface of the villi (p. 331).
During digestion in the small intestine, the villi become:
turgid with blood, their epithelial cells become filled, by
absorption, with fat-globules, which, after minute division,
transude into the granular basis of the villus, and thence
into the lacteal vessel in the centre, by which they are
conveyed along the mesentery to the lymphatic glands,
and thence into the thoracic duct. <A part of the fat is
also absorbed by the blood-vessels of the intestine. The
term chyle is sometimes applied to the emulsified contents.
of the intestine after their admixture with the bile and
pancreatic juice; but more strictly to the fluid contained in
the lacteal vessels during digestion, which differs from
ordinary lymph contained in the same vessels at other times,

——
ee

2x Asedsr.«

= ee

= ee eel

ey re

' DIGESTION IN SMALL INTESTINE, 339

chiefly in the greatly increased quantity of fat particles
which have been absorbed from the small intestine.

Although the most evident function of the small intes-
tine is the digestion of fat, it must not be forgotten that
a great part of the other constituents of the food is by no
means completely digested when it leaves the stomach.
Indeed, its leaving it unabsorbed would, alone, be proof of
this fact.

The albuminous substances which have been partly dis-
solved in the stomach continue to be acted on by the
gastric juice which passes into the duodenum with them,
and the effect of the last-named secretion is assisted or
complemented by that of the pancreas and intestinal
glands. As the albuminous matters are dissolved, they
are absorbed chiefly by the blood-vessels, and only to a
small extent, probably, by the lacteals.

The starchy, or amylaceous portion of the food, the con-
version of which into dextrin and sugar was more or less
interrupted during its stay in the stomach, is now acted
on briskly by the secretion of the pancreas, and of Brunn’s
glands, and pzrhaps of Lieberkiihn’s glands also, and the
sugar as it is formed dissolves in the intestinal fluids, and
afterwards, like the albumen, is absorbed chiefly by the
blood-vessels.

The liquids, swallowed as such, which may have escaped
absorption in the stomach, are absorbed probably very
soon after their entrance into the intestine; the fluidity of
the contents of the latter being preserved more by the con-
stant secretion of fluid by the intestinal glands, pancreas,
and liyer, than by any given portion of fluid, whether
swallowed or secreted, remaining long unabsorbed. From
this fact, therefore, it may be gathered that there is a
kind of circulation constantly proceeding from the intestines
into the blood, and from the blood into the intestines
again ; for, as all the fluid, probably a very large amount,
secreted by the intestinal glands, must come from the

Z% 2

~

340 DIGESTION.

blood, the latter would be too much drained, were it not
that the same fluid after secretion is again re-absorbed
into the current of blood—going into the blood charged
with nutrient products of digestion—coming out again by
secretion through the glands in in a comparatively uncharged
condition.

It has been said before that the contents of the stomach
during gastric digestion have a strongly acid reaction.
On the entrance of the chyme into the small intestine,
this is gradually neutralized to a greater or less degree by
admixture with the bile and other secretions with which
it is mixed, and the acid reaction becomes less and less
strongly marked as the chyme passes along the canal
towards the ileo-ceecal valve.

Thus, all the materials of the food are anted on in the
small intestine, and a great portion of the nutrient matter
is absorbed—the fat chiefly by the Jlacteals, the other
principles, when in a state of solution, chiefly by the blood-
vessels, but neither, probably, exclusively by one set of
vessels. At the lower end of the small intestine, the chyme,

still thin and pultaceous, is of a light yellow colour, and

has a distinctly feecal odour. In this state it passes
_ through the ileo-ceecal opening into the large intestine.

Summary of the Process of Digestion in the Large Intestine.

The changes which take place in the chyme after its
passage from the small into the large intestine are probably
only the continuation of the same changes that occur in
the course of the food’s passage through the upper part of
the intestinal canal. From the absence of villi, however,
we may conclude that absorption, especially of fatty
matter, is in great part completed in the small intestine,
while, from the still half-liquid, pultaceous consistence of
the chyme when it first enters the czecum, there can be no
doubt that the absorption of liquid is not by any means

J
a

rer 7

ee es te eas ee

SS ae

DIGESTION OF LARGE INTESTINE. 341

concluded. The peculiar odour, moreover, which is

acquired after a short time by the contents of the large

bowel, would seem to indicate the addition to them, in
this region, of some special matter, probably excretory.
The acid reaction, which had become less and less distinct
in the small bowel, again becomes very manifest in the
czecum—probably from acid fermentation processes in some
of the materials of the food.

There seems no reason, however, to conclude that any
special, ‘ secondary,’ digestive process occurs in the cecum
or in any other part of the large intestine. Probably any ©
constituent of the food which has escaped digestion and
absorption in the small bowel may be digested in the large
intestine ; and the power of this part of the intestinal
canal to digest fatty, albuminous, or other matters, may
be gathered from the good effects of nutrient enemata, so
frequently given when from any cause there is difficulty in
introducing food into the stomach. In ordinary healthy
digestion, however, the changes which ensue in the chyme.
after its passage into the large intestine, are mainly the
absorption of the more. liquid parts, and the addition of
the special excretory products which give it the charac-
teristic odour. At the same time, as before said, it is
probable that a certain quantity of nutrient matter always
escapes digestion in the small intestine, and that this
happens more especially when food has been taken in
excess, or when it is of such a kind as to be difficult of
digestion. Under these circumstances there is no doubt
that such changes as were proceeding in it at the lower
part of the ileum may go on unchecked in the large bowel,
—the process being assisted by the secretion of the nume-
rous tubular glands therein present,

By these means the contents of the large intestine, as
they proceed towards the rectum, become more and more
solid, and losing their more liquid and nutrient parts,
gradually acquire the odour and consistence characteristic

342 DIGESTION.

of feces. After a sojourn of uncertain duration in the.
rectum, they are finally expelled by the contraction of its
muscular coat, aided, under ordinary circumstances, by the
contraction of the abdominal muscles.

For a description of the mechanism by which the act of ©

defeecation is accomplished, see p. 223.

The average quantity of solid feecal matter evacuated by
the human adult in twenty-four hours is about five ounces;
an uncertain proportion of which consists simply of the
undigested or chemically modified residue of the food
and the remainder of certain matters which are excreted
in the intestinal canal. |

Composition of Faces.

Water . é ; ; : : ‘ : . ‘ 733°00
Solids. , . : . ' ; . SS 267°00

Special excrementitious constituents :— Excretin, \
excretoleic acid (Marcet), and_ stercorin
(Austin Flint).

Salts :—Chiefly phosphate of magnesia and phos-
phate of lime, with small quantities of iron,
soda, lime, and silica.

Insoluble residue of the food (chiefly starch,
grains, woody tissue, particles of cartilage,
and fibrous tissue, undigested muscular fibres
or fat, and the like), with insoluble substances
accidentally introduced with the food.

Mucus, epithelium, altered colouring matter of
bile, fatty acids, etc. . ;

267 00

say

The time occupied by the journey of a given portion of
food from the stomach to the anus, varies considerably even
in health, and on this account, probably, it is that such
different opinions have been expressed in regard to the
subject. Dr. Brinton supposes twelve hours to be occupied
by the journey of an ordinary meal through the small intes-

——

Ce ee ee ae a ee

GASES OF INTESTINAL CANAL. 343

tine, and twenty-four to thirty-six hours by the passage
through the large bowel.

On the Gases contained in the Stomach and Intestines.

It need scarcely be remarked that, under ordinary cir-
cumstances, the alimentary canal contains a considerable
quantity of gaseous matter. Any one who has had occa-
sion, in a post-mortem examination, either to lay open the
intestines, or to let out the gas which they contain, must
have been struck by the small space afterwards occupied
by the bowels, and by the large degree, therefore, in which
the gas, which naturally distends them, contributes to fill
the cavity of the abdomen. Indeed, the presence of air in
the intestines is so constant, and, within certain limits, the
amount in health so uniform, that there can be no doubt
that its existence here is not a mere accident, but intended
to serve a definite and important purpose, although, pro-
bably, a mechanical one.

The sources of the gas contained in the stomach and
bowels may be thus enumerated—

1. Air introduced in the act of swallowing either food or
saliva.

2. Gases developed by the decomposition of alimentary
matter, or of the secretions and excretions mingled with it
in the stomach and intestines.

3. It is probable that a certain mutual interchange
occurs between the gases contained in the alimentary
canal, and those present in the blood of the gastric and in-
testinal blood-vessels ; but the conditions of the exchange
are not known, and it is very doubtful whether anything
like a true and definite secretion of gas from the blood
into the intestines or stomach ever takes places. There can
be no doubt, however, that the intestines may be the
proper excretory organs for many odorous and other sub-
stances, either absorbed from the air taken into the lungs

344 ‘ DIGESTION.

in inspiration, or absorbed in the upper part of the
alimentary canal, again to be excreted at a portion of the
same tract lower down—in either case assuming rapidly

a gaseous form after their excretion, and in this way,

perhaps, obtaining a more ready egress from the body.

It is probable that, under ordinary circumstances, the
gases of the stomach and intestines are derived chiefly from
the second of the sources which have been enumerated.

- Tabular Analysis of Gases contained in the Alimentary Canal.

Composition by Volume.
Whence obtained. | basal Ku .
: arbon. Carburet. |Sulphure
Oxygen, Nitrog. | Acid, | #¥drog ‘Hydrogen,| Hydrogen.
Stomach ERTS 71 14 4 | — —
Small Intestine .| — 32 30 38 | —
Cecum . a 66 12 8 13 fue
Colon —- 35 57 6 8 Bens
Rectum. ye a ee 46 43 — | Il.
Expelledperanum | — 22 41 19 | 19 4

The above tabular analysis of the gases contained in the
alimentary canal has been quoted from the analyses of
Jurine, Magendie, Marchand, and Chevreul by Dr. Brinton,
. from whose work the above enumeration of the sources of
the gas has been also taken.

Movements of the Intestines.

It remains only to consider the manner in which the
food and the several secretions mingled with it are
moved through the intestinal canal, so as to be slowly
subjected to the influence of fresh portions of intestinal
secretion, and as slowly exposed to the absorbent power
of all the villi and blood-vessels of the mucous mem-
brane. The movement of the intestines is peristaltic

shat

cin dt ilie gee et llanteniee 5: Caml tated is

.
we ee a eS re ae

”

'
MOVEMENTS OF THE INTESTINES. 345

or vermicular, and is effected by the alternate con-
tractions and dilatations of successive portions of the
intestinal coats. The contractions, which may commence
at any point of the intestine, extend in a wave-like
manner along the tube. In any given portion, the longi-
tudinal muscular fibres contract first, or more than the
circular ; they draw a portion of the intestine upwards; or,
as it were, backwards, over the substance to be propelled,
and then the circular fibres of the same portion contracting
in succession from above downwards, or, as it were, from
behind forwards, press on the substance into the portion
next below, in which at once the same succession of actions
next ensues. These movements take place slowly, and, in
health, are commonly unperceived by the mind; but they
are perceptible when they are accelerated under the influ-
ence of any irritant.

The movements of the intestines are sometimes retro-
grade; and there is no hindrance to the backward move-
ment of the contents of the small intestine. But almost
complete security is afforded against the passage of the
contents of the large into the small intestine by the ileo-
ceecal valve. Besides, —the orifice of . communication
between the ileum and cecum (at the borders of which
orifice are the folds of mucous membrane which form
the valve) is encircled with muscular fibres, the con-
traction of which prevents the undue dilatation of the
orifice.

Proceeding from above downwards, the muscular fibres
of the large intestine become, on the whole, stronger in
direct proportion to the greater strength required for the
onward moving of the feeces, which are gradually becoming
firmer. The greatest strength is in the rectum, at the
termination of which the circular unstriped muscular fibres
form a strong band called the internal sphincter, while an
external sphincter muscle with striped fibres is placed rather
lower down, and more externally, and holds the orifice close

346 DIGESTION.

by a constant slight contraction under the influence of the
spinal cord.

The peculiar condition of the sphincter, in relation to the
nervous system, will be again referred to. The remaining
portion of the intestinal canal is under the direct influence
of the sympathetic or ganglionic system, and indirectly, or
more distantly, is subject to the influence of the brain and
spinal cord, which influence appears to be, in some degree,
transmitted through the vagus nerve. Experimental irri-
tation of the brain or eord produces no evident or constant
effect on the movements of the intestines during life; yet
in consequence of certain conditions of the mind, the move-
ments are accelerated or retarded; and in paraplegia the
intestines appear after a time much weakened in their
power, and costiveness, with a tympanitic condition, ensues.
Immediately after death, irritation of both the sympathetic
and pneumo-gastric nerves, if not too strong, induces
genuine peristaltic movements of the intestines. Violent
irritation stops the movements. These stimuli act, no
doubt, not directly on the muscular tissue of the intestine,
but on the rich ganglionic structure shown by Meissner to
exist in the sub-mucous tissue. This regulates and controls
the movements, and gives to them their peculiar slow,
orderly, rhythmic, and peristaltic character, both naturally,
and when artificially excited.

a@ ths

ae fr oe

Be Sa

347

CHAPTER X.

ABSORPTION.

Tue process of absorption has, for one of its objects, the
introduction into the blood of fresh materials from the
food and air, and of whatever comes into contact with the
external or internal surfaces of the body; and, for another,
the taking away of parts of the body itself, when, having
fulfilled their office, or otherwise requiring removal, they
need to be renewed. In both these offices, i.e., in both
absorption from without and absorption from within, the
process manifests some variety, and a very wide range of
action; and in both it is probable that two sets of vessels
are, or may be, concerned, namely, the blood-vessels, and
the lacteals or lymphatics, to which the term absorbents
has been especially applied.

Structure and Office of the Lacteal and Lymphatic Vessels and
Glands.

Besides the system of arteries and veins, with their inter-
mediate vessels, the capillaries, there is another system of
canals in man and other vertebrata, called the lymphatic
system, which contains a fluid called lymph. Both these
systems of vessels are concerned in absorption.

The principal vessels of the lymphatic system are, in
structure and general appearance, like very small and thin-
walled veins, and like them are provided with valves. By
one extremity they commence by fine microscopic branches,
the lymphatic’ capillaries or lymph-capillaries, in the organs
and tissues of nearly every part of the body, and by their
other extremities they end directly or indirectly in two
trunks which open into the large veins near the heart (fig.
92). Their contents, the lymph and chyle, unlike the blood,

348 ABSORPTION.

pass only in one direction, namely, from the fine branches
to the trunk and so to the large veins, on entering which
they are mingled with the stream of blood, and form part

Fig. 92.*

Lymphaties of head

Lymphatics of head and neck, left.

and neck, right.

; Thoracic duct
Right internal jug-
ular vein. _
Right subclavian Left subclavian vein.
Vein. -

Lymphatics ofright
arm,

Thoracic duct.

Receptaculum chyli.
Lacteals

Lymphatics of lower

Lymphatics of lowe
extremities,

extremities.

of its constituents, Remembering the course of the fluid
in the lymphatic vessels, viz., its passage in the direction
only towards the large veins in the neighbourhood of the
heart, it will be readily seen from fig. 92 that the greater
part of the contents of the lymphatic system of vessels passes

* Fig. 92. Diagram of the principal groups of lymphatic vessels
‘from Quain).

COURSE OF THE LYMPHATICS. 349

through a comparatively large trunk called the thoracic

duct, which finally empties its contents into the blood-stream
at the junction of the internal jugular and subclavian veins
of the left side. There is a smaller duct on the riyht side.
The lymphatic vessels of the intestinal canal are called
lacteals, because, during digestion, the fluid contained in
them resembles milk in appearance ; and the lymph in the
lacteals during the period of digestion is called chyle.
There is no essential distinction, however, between lacteuls
and lymphatics. | }

In some part of their course all lymphatic vessels pass
through certain bodies called lymphatic giands.

Lymphatic vessels are distributed in nearly all parts of
the body. Their existence, however, has not yet been
determined in the placenta, the umbilical cord, the mem-
branes of the ovum, or in any of the non-vascular parts,
as the nails, cuticle, hair, and the like.

_ The lymphatic capillaries commence most commonly
either in closely-meshed networks, or in irregular lacunar
spaces between the various structures of which the dif-
ferent organs are composed. The former is the rule of
origin with those lymphatics which are placed most super-
ficially, as, for instance, immediately beneath the skin, or
under the mucous and serous membranes; while the latter
is most common with those which arise in the substance of
organs. In the former instance, their walls are composed
of but little more than homogeneous membrane, lined by
a single layer of epithelial cells, very similar to those
which line the blood-capillaries (fig. 49). In the latter
instance the small irregular channels and spaces from
which the lymphatics take their origin, although they are
formed mostly by the chinks and crannies between the
blood-vessels, secreting ducts, and other parts which may
happen to form the framework of the organ in which they
exist, yet have also a layer of epithelial cells to define and
bound them.

350 ABSORPTION.

The lacteals appear to offer an illustration of another
mode of origin, namely, in blind dilated extremities (figs.

Fig. 93.*

* Fig. 93. Lymphatic vessels of the head and neck of the upper
part of the trunk (from Mascagni). %.—The chest and pericardium have
been opened on the left side, and the left mamma detached and thrown
outwards over the left arm, so as to expose a great part of its deep
surface. The principal lymphatic vessels and glands are shown on the
side of the head and face, and in the neck, axilla, and mediastinum.
Between the left internal jugular vein and the common carotid artery,
the upper ascending part of the thoracic duct marked 1, and above
this, and descending to 2, the arch and last part of the duct. The
termination of the upper lymphatics of the diaphragm in the medi-
astinal glands, as wellas the cardiac and the deep mammary lymphatics,
are also shown.

ail bd
a a Pes

35%

ORIGIN OF LYMPHATICS.

tructure

aries of other parts.

in s
es seem likely to put an end soon to the

tial difference

but there is no essen

?

81, 82)

ic capi

between these and the lymphat

iscoveri

Recent d

Mane ee sisslating

rs Se ll

Superficial lymphatics of the forearm and palm of the’

* Fig. 94.
hand, 4 (after Mascagni).

5. Two small glands at the bend of the

7. Ulnar lymphatic vessels,
9, 9’. Outer and inner sets of vessels..

6. Radial lymphatic vessels.

arm.

8, 8. Palmar arch of lymphatics.

352 ABSORPTION.

long-standing discussion whether any direct communications
exist between the lymph-capillaries and blood-capillaries ;
the need for any special intercommunicating channels seem-
ing to disappear in the light of more accurate knowledge of
the structure and endowments of the parts concerned. For
while, on the other hand, the fluid part of the blood con-
stantly exudes or is strained through the walls of the blood-
capillaries, so as to moisten all the surrounding tissues,
and occupy the interspaces: which exist among their
different elements, these same interspaces have been shown,
as just stated, to form the beginnings of the lymph-capil-
laries. And while, for many years, the notion of the
existence of any such channels between the blood-vessels
and lymph-vessels, as would admit blood-corpuscles, has
been given up, recent observations have proved that, for
the passage of such corpuscles, it is not necessary to assume
the presence of any special channels at all, inasmuch as

blood-corpuscles can pass bodily, without much difficulty, —

through the walls of the blood-capillaries and small veins
(p. 164), and could pass with still less trouble, probably,
through the comparatively ill-defined walls of the capillaries
which contain lymph. ;

Observations of Recklinghausen have led to the dis-
covery that in certain parts of the body openings exist
by which lymphatic capillaries directly communicate with
parts hitherto supposed to be closed cavities. If the peri-
toneal cavity be injected with milk, an injection is obtained
of the plexus of lymphatic vessels of the central tendon of
the diaphragm ; and on removing a small portion of the
central tendon, with its peritoneal ,surface uninjured, and

b. Cephalic vein. d. Radial vein. e¢. Median vein. jf. Ulnar vein.
The lymphatics are represented as lying on the deep fascia.

+ Fig. 95. Superficial lymphatics of right groin and upper part of
thigh, $ (after Mascagni). 1. Upper inguinal glands. 2’. Lower in-
guinal or femoral glands, 3, 3. Plexus of lymphatics in the course of
the long saphenous vein.

ey. ee

ee eee ee

ee eet ee Fn

STRUCTURE OF LYMPHATIC VESSELS. 353

examining the process of absorption under the micro-
scope, Recklinghausen noticed that the milk-globules ran
towards small natural openings or stomata between the
epithelial cells, and disappeared by passing vortex-like
through them. The stomata, which had a roundish outline,
were only wide enough to admit two.or three milk-globules
abreast, and never exceeded the size of an epithelial cell.
Openings of a similar kind have been found by Dybskowsky
in the pleura; and as they may be presumed to exist in
other serous membranes, it would seem as if the serous
cavities, hitherto supposed closed, form but a large widen-
ing out, so to speak, of the lymph-capillary system with
which they directly communicate.

In structure, the medium-sized and larger lymphatic
vessels are very like veins; having, according to Kdélliker,
an external coat of fibro-cellular tissue, with elastic
filaments; within this, a thin layer of fibro-cellular
tissue, with organic muscular fibres, which have, princi-
pally, a circular direction, and are much more abundant in
the small than in the larger vessels; and again, within
this, an inner elastic layer of longitudinal fibres, and a
lining of epithelium; and numerous valves. The valves,
constructed like those of veins, and with the free edges
turned towards the heart, are usually arranged in pairs,
and, in the small vessels, are so closely placed, that when
the vessels are full, the valves constricting them where
their edges are attached, give them a peculiar braided or
knotted appearance (fig. 99).

With the help of the valvular mechanism, all occasional
pressure on the exterior of the lymphatic and lacteal ves-
sels propels the lymph towards the heart: thus muscular
and other external pressure accelerates the flow of the
lymph as it does that of the blood in the veins (see p. 170).
The actions of the muscular fibres of the small intestine,
and probably the layer of organic muscle present in each

intestinal villus (p. 307), seem to assist in propelling the
ee oP

a\«

354. ABSORPTION,

chyle: for, in the small intestine of a mouse, Poiseuille
saw the chyle moving with intermittent propulsions that
appeared to correspond with the peristaltic movements of
the intestine. But for the general propulsion of the lymph

and chyle, it is probable that, together with the vis a tergo —
resulting from absorption (as in the ascent of sap in

a tree), and from external pressure, some of the force may
be derived from the contractility of the vessel’s own walls.
Kolliker, after watching the lymphatics in the transparent
tail of the tadpole, states that no distinct movements of
their walls can ever be seen, but as they are emptied after
death they gradually contract, and then, after some time,
again dilate to their former size, exactly as the small
arteries do under the like circumstances. Thus, also, the
larger vessels in the human subject commonly empty
themselves after death; so that, although absorption is
probably usually going on just before the time of death, it
is not common to see the lymphatic or lacteal vessels full.
Their power of contraction under the influence of stimuli
has been demonstrated by Kolliker, who applied the wire
of an electro-magnetic apparatus to some well-filled
lymphatics on the skin of a boy’s foot, just after the re-
moval of his leg by amputation, and noticed that the
calibre of the vessels diminished at least one half. It is
most probable that this contraction of the vessels occurs
during life, and that it consists, not in peristaltic or undu-
latory movements, but in an uniform contraction of the
successive portions of the vessels, by which pressure is
steadily exercised upon their contents, and which alternates

’ with their relaxation.

Lymphatic Glands.

Almost all lymphatic and lacteal vessels in some part of
their course pass through one or more small bodies called
lymphatic glands (fig. 99).

A lymphatic gland is covered externally by a capsule of

er

<<, Poe

as

——

ane ee ee

LYMPHATIC GLANDS. . 355

connective tissue, which invests and supports the glandular
structure within; while prolonged from its inner surface
are processes or trabecule which, entering the gland from
all sides, and freely communicating, form a fibrous scaf-
folding or stroma in all parts of the interior. Thus are
formed in the outer or cortical part of the glands (fig. 96)
in the intervals of the
trabeculee, certain inter-
communicating spaces
termed alveoli; while
a finer meshwork is /”
formed in the more cen-
tral or medullary part. “
In the alveoli and the
trabecular meshwork the
proper gland substance
is contained ; in the form of nodules in the cortical alveoli,
and of rounded cords in the medullary part (fig. 97).
The gland-substance of one part is continuous directly
or indirectly with that of all others.

The essential structure of lymphatic-gland substance
resembles that which was described as existing, in a simple
form, in the interior of the solitary and agminated intes-
tinal follicles (p. 302). Pervading all parts of it, and
occupying the alveoli and trabecular spaces before referred
to, is a network of the variety of connective tissue termed
retiform tissue (fig. 98), the interspaces of which are
occupied by lymph-corpuscles. The corpuscles are ar-
ranged in such a way, that while in the centre of the
alveoli and of each mesh they are so crowded together
as to be, with the retiform tissue pervading them, a con-

* Fig. 96 (after Kolliker). Section of a mesenteric gland from the
ox, slightly magnified. a, hilus; 0 (in the central part of the figure),
medullary substance ; c, cortical substance with indistinct alveoli; d,

capsule,
AA2

356 - ABSORPTION.

sistent gland-pulp, continuous in the form of the nodules
and cords, before referred to, throughout the whole gland,
they are in comparatively small numbers in the outer part
of the alveoli and meshes, and leave this portion, as it
were, open. (See figs. 97, 98.) This free space between
the gland-pulp and the trabecular stroma, occupied only by
retiform tissue, is called the lymph-channel or lymph-path,
because it is traversed by the lymph, which is continually
brought to the gland and conveyed away from it by

Fig. 97.*

2

=
S
S

mn)
ee, G

Re
lymphatic vessels; those which bring it being termed
afferent vessels, and those which take it away efferent
vessels. The former enter the cortical part of the gland
and open ifito its alveoli, at the same time that they lay
aside all their coats except the epithelial lining, which may
be said to continue to line the lymph-path into which the

* Fig. 97. Section of Medullary Substance of an Inguinal Gland
of an Ox (magnified 90 diameters). a, a, glandular substance or
pulp forming rounded cords joining in a continuous net (dark in the
figure) ; ¢, ¢c, trabecule ; the space, 0, b, between these and the gland-
ular substance is the lymph-sinus, washed clear of corpuscles and
traversed by filaments of retiform connective tissue (after Kolliker).

—e we

LYMPHATIC GLANDS. - 357

contents of the afferent vessels now pass. The efferent
vessels begin in the medullary part of the gland, and are
continuous with the lymph-path here as the afferent vessels
were with the cortical portion; the epithelium of one is
continuous with that of the other.

Blood-vessels are freely distributed to the trabecular
tissue and to the gland-pulp (fig. 98).

Properties of Lymph and Chyle.

The fluid, or lymph, contained in the lymphatic vessels
| Fig. 98*

is, under ordinary circumstances, clear, transparent, and

* Fig. 98. A Small Portion of Medullary Substance from a Mesen-
teric Gland of the Ox (magnified 300 diameters). d, d, trabecule ; a,
part of a cord of glandular substances from which all but a few of
the lymph-corpuscles have been washed out to show its supporting
meshwork of retiform tissue and its capillary blood-vessels (which have
been injected, and are dark in the figure) ; }, b, lymph-sinus, of which
the retiform tissue is represented only at c, c (after Kélliker).

358 ABSORPTION.

colourless, or of a pale yellow tint. It is devoid of smell,
is slightly alkaline, and has a saline taste. As seen with
the microscope in the small transparent vessels of the tail
of the tadpole, the lymph usually contains no corpuscles or
particles of any kind; and it is probably only in the larger
trunks in which, by a process similar to that to be described
in the chyle, the lymph is more elaborated, that any cor-

puscles are formed. ‘These corpuscles are

similar to those in the chyle, but less nume-
\7, rous. The fluid in which the corpuscles float
is commonly and in health albuminous, and
contains no fatty particles or molecular base ;
but it is liable to variations according to the
general state of the blood, and that of the
organ from which the lymph is derived. As
it advances towards the thoracic duct, and
passes through the lymphatic glands, it be-
comes, like chyle, spontaneously coagulable
from the formation of fibrin, and the number
of corpuscles is much increased.

The fluid contained in the lacteals, or
lymphatic vessels of the intestine, is clear
and transparent during fasting, and differs
in no respect from ordinary lymph; but
during digestion, it becomes milky, and is
termed chyle.

Chyle is an opaque, whitish fluid, resem-
bling milk in appearance, and having a neu-
tral or slightly alkaline reaction. Its white-
ness and opacity are due to the presence
of innumerable particles of oily or fatty matter, of exceed-
ingly minute though nearly uniform size, measuring on the
average about >;45,5 of an inch (Gulliver). These con-
stitute what Mr. Gulliver appropriately terms the molecular

Fig. 99.*

* Fig. 99. A lymphatic gland from the axilla, with its afferent and
efferent vessels, injected with mercury (after Bendz).

Pe ee ee

CHYLE. 359

base of chyle. Their number, and consequently the opacity
of the chyle, are dependent upon the quantity of fatty
matter contained in the food. Hence, as a rules, the chyle
is whitish and most turbid in carnivorous animals; less so
in Herbivora; while in birds it is usually transparent.
The fatty nature of the molecules is made manifest by
their solubility in ether, and, when the ether evaporates,
by their being deposited in various-sized drops of oil.*
Yet, since they do not run together and form a larger
drop, as particles of oil would, it appears very probable
that each molecule consists of oil coated over with albu-
men, in the manner in which, as Ascherson observed, oil
always becomes covered when set free in minute drops in
an albuminous solution. And this view is supported by
the fact, that when water or dilute acetic acid is added to
chyle, many of the molecules are lost sight of, and oil-
drops appear in their place, as if the investments of the
molecules had been dissolved, and their oily contents had
run together.

Except these molecules, the chyle taken from the villi
or from lactvals near them, contains no other solid or
organized bodies. The fluid in which the molecules float
is albuminous, and does not spontaneously coagulate,
though coagulable by the addition of ether. But as the
chyle passes on towards the thoracic duct, and especially
while it traverses one or more of the mesenteric glands
(propelled by forces which have been described with the
structure of the vessels), it is elaborated. The quantity of
molecules and oily particles gradually diminishes; cells, to
which the name of chyle-corpuscles is given, are developed
in it; and by the formation of fibrin, it acquires the pro-
perty of coagulating spontaneously. The higher in the

* Some of the molecules may remain undissolved by the ether ; but
this appears to be due to their being defended from the action of the
ether by being entangled within the albumen which it coagulates.

360 ABSORPTION.

—

-

thoracic duct the chyle advances, the more is it, in all
these respects, developed; the greater is the number of
chyle-corpuscles, and the larger and firmer is the clot
which forms in it when withdrawn and left at rest. Such
a clot is like one of blood, without the red corpuscles,

having the chyle-corpuscles entangled in it, and the fatty

matter forming a white creamy film on the surface of the
serum. But the clot of chyle is softer and moister than
that of blood. Like blood, also, the chyle often remains
for a long time in its vessels without coagulating, but
coagulates rapidly on being removed from them (Bouisson).
The existence of fibrin, or of the materials which, by their
union form it (p. 65 et seq.), is, therefore, certain; its
increase appears to be commensurate with that of the
corpuscles; and, like them, it is not absorbed as such from
the chyme (for no fibrin exists in the chyle in the villi),
but is gradually elaborated out of the albumen which chyle,
in its earliest condition, contains.

The structure of the chyle-corpuscles was described
when speaking of the white corpuscles of the blood, with
which they are identical.

From what has been said, it will appear that perfect
chyle and lymph are, in essential characters, nearly similar,
and scarcely differ, except in the preponderance of fatty
matter in the chyle. The comparative analysis of the two
fluids obtained from the lacteals and the lymphatics of a
donkey is thus given by Dr. Owen Rees :—

Chyle. Lymph.

Water ; : : . : , 90°237 96°536
Albumen. ; : : ye 3516 1°200
Fibrin : : ; ; ; 0°370 0°120
Animal extractive. * ; on 1°565 1°559
Fatty matter. ; ; . ‘ 3601 a trace.
Salts . : ; ; : . ‘ o’711 0°585

100*000 100’000
The analyses of Nasse afford an estimate of the rela-

\

eae

ae — ae ee

COMPOSITION OF LYMPH AND CHYLE. 361

tive compositions of the lymph, chyle, and blood of the
horse.*

Lymph. Chyle. Blood.
Water. ? ; $950C 935° 810°
Corpuscles . ‘ pave 4° 92°8
Albumen ; , a ae ae 31° 80°
Fibrin : . jae 0°75 2°8
Extractive matter . ; 4°88 6°25 52
Fatty matter. 5 bs 0°09 15° 1°55
Alkaline salts : ; 5°61 1% 6°7

phate of limeand mag-

Tae Eb ssce3Rcoy aR ts sR

1000° 1000° 1000.

The contents of the thoracic duct, including both the
lymph and chyle mixed, in an executed criminal, were
examined by Dr. Rees, who found them to consist of—

Water . , : F : athe . . . 90°48
Albumen and fibrin . : : ‘ ‘ Kies 7°08
Extractive matter... ; , : ‘ : o°108
Fatty As : : ; ; : fer 0'92
Saline . : ‘ ‘ é ; ‘ «i VOM

From all these analyses of lymph and chyle, it appears
that they contain-essentially the same organic constituents
that are found in the blood, viz., albumen, fibrin, and fatty
matter, the same saline substances, and iron. Their com-
position differs from that of the blood in degree rather than
in kind; they contain a less proportion of all the substances
dissolved in the water (see Nasse’s analyses, just quoted),
and much less fibrin. ‘The fibrin} of lymph, besides being
less in quantity, appears to be in a less elaborated state
than that of the blood, coagulating less rapidly and less
firmly. According to Virchow, it never coagulates, under

* The analysis of the blood differs rather widely from that given at
page 78; but if it be erroneous, it is probable that corresponding errors
exist in the analysis of the lymph and chyle ; and that therefore the
tables in the text may represent accurately enough the relation in which
the three fluids stand to each other.

t For observations on the nature of fibrin, see p. 65.

362 ABSORPTION.

ordinary circumstances, within the lymphatic vessels, either

during life or after death. These differences gradually

diminish, while the lymph and chyle, passing towards and
through the thoracic duct, gradually approach the place at
which they are to be mingled with the blood. For, in the
thoracic duct, besides the higher and more abundant
development of the fibrin, the lymph and chyle-corpuscles
are found more advanced towards their development into
red-blood corpuscles; sometimes even that development is
completed, and the lymph has a pinkish tinge from the
number of red blood-corpuscles that it contains.

The general result, therefore, of both the microscopic
and the chemical: examinations of the lymph and chyle,
demonstrate that they are rudimental blood; their fluid
part being, like the liquor sanguinis, diluted, but gradually
becoming more concentrated; and their corpuscles being
in process of development into red blood-corpuscles. Thus,
in quality, the lymph and chyle are adapted to replenish
the blood; and their quantity, so far as it can be estimated,
appears ample for this purpose. In one of Magendie’s
experiments, half an ounce of chyle was collected in five
minutes from the thoracic duct of a middle-sized dog ;
Collard de Martigny obtained nine grains of lymph, in ten
minutes from the thoracic duct of a rabbit which had
taken no food for twenty-four hours; and Gieger, from
three to five pounds of lymph daily from the foot of a

horse, from whom the same quantity had been flowing —

several years without injury to health. Bidder found, on
opening the thoracic duct in cats, immediately after death,
that the mingled lymph and chyle continued to flow from
one to six minutes; and, from the quantity thus obtained,
he estimated that if the contents of the thoracic duct con-
tinued to move at the same rate, the quantity which would
pass into a cat’s blood in twenty-four hours would be equal
to about one-sixth of the weight of the whole body. And,
since the estimated weight of the blood in cats is to the

se my

4
i
%
E
A
«
Fs

QUANTITY OF LYMPH AND CHYLE. 363

weight of their bodies as I : 7, the quantity of lymph daily
traversing the thoracic duct would appear to be about
equal to the quantity of blood at any time contained in the
animals. Schmidt’s observations on foals have yielded
very similar results. By another series of experiments,
Bidder estimated that the quantity of lymph >traversixfg
the thoracic duct of a dog in twenty-four hours is about
equal to two-thirds of the blood in the body. If we take
these estimates, it will not follow from them that the whole
of an animal’s blood is daily replaced by the development
of lymph and chyle; for even if the quantity of lymph
and chyle daily formed be equal to that of the blood, the
solid contents of the blood will be much too great to be
replaced by those of the lymph and chyle. According to
Nasse’s analyses, the solid matter of a given quantity of
blood could not be replaced out of less than three or four
times the quantity of lymph and chyle. |

Absorption by the Lacteal Vessels.

During the passage of the chyme along the whole tract
of the intestinal canal, its completely digested parts are
absorbed by the blood-vessels and lacteals distributed in
the mucous membrane. The blood-vessels appear to
absorb chiefly the dissolved portions of the food, and
these, including especially the albuminous and saccharine,
they imbibe without choice; whatever can mix with the
blood passes into the vessels, as will be presently described.
But the lacteals appear to absorb only certain constituents
of the food, including particularly the fatty portions. The
absorption by both sets of vessels is carried on most
actively, but not exclusively, in the villi of the small intes-
tine; for in these minute processes, both the capillary
blood-vessels and the lacteals are brought almost into
contact with the intestinal contents.

It has been already stated that the villi of the small
intestine (figs. 81 and 82), are minute vascular processes

364. ABSORPTION.

of mucous membrane, each containing a delicate net-
work of blood-vessels and one or more lacteals, and are
invested by a sheath of cylindrical epithelium. In the
interspaces of the mucous membrane between the villi, as
well as over all the rest of the intestinal canal, the lacteals
and blood-vessels are also densely distributed in a close net-
work, the lacteals, however, being more sparingly supplied
to the large than to the small intestine.

There seems to be no doubt that absorption of fatty
matters during digestion, from the contents of the intes-
tines, is effected chiefly by the epithelial cells which line
the intestinal tract, and especially by those which clothe
the surface of the villi (fig. 81). From these epithelial
cells, again, the fatty particles are passed on into the inte-
rior of the lacteal vessels (figs. 81 and 82), but how they
pass, and what laws govern their so doing, are not at pre-
sent exactly known.

It is probable that the process of absorption by the epi-
thelial cells, is assisted by the pressure exercised on the
contents of the intestines by their contractile walls; and
that the absorption of fatty particles is also facilitated by
the presence of the bile, the pancreatic and intestinal se-
cretions which moisten the absorbing surface. For it has
been found by experiment, that the passage of oil through
an animal membrane is made much easier when the latter
is impregnated with an alkaline fluid.

Absorption by the Lymphatic Vessels.

The real source of the lymph, and the mode in which its
absorption is effected by the lymphatic vessels, were
long matters of discussion. But the problem has been
much simplified by more accurate knowledge of the anato-
mical relations of the lymphatic capillaries. It is most
probable that the lymph is derived, in great part, from the
liquor sanguinis, which, as before remarked, is always
exuding from the blood-capillaries into the interstices of

el

ABSORPTION BY LYMPHATICS. 365
the tissues in which they lie; and changes in the cha-
racter of the lymph correspond very closely with changes
in the character of either the whole mass of blood, or of
that in the vessels of the part from which the lymph is
examined. Thus Herbst found that the coagulability of
the lymph is directly proportionate to that of the blood;
and that when fluids are injected into the blood-vessels
in sufficient quantity to distend them, the injected sub-
stance may be almost directly afterwards found in the
lymphatics.

It is not improbable, however, that some other matters
than those originally contained in the exuded liquor san-
guinis may find their way with it into the lymphatic
vessels. Parts which having entered into the composition
of a tissue, and, having fulfilled their purpose, require to
be removed, may not be altogether excrementitious, but
may admit of being re-organised and adapted again for
nutrition ; and these may be absorbed by the lymphatics,
and elaborated with the other contents of the lymph in
passing through the glands.

Lymph-Hearts. In reptiles and some birds, an important
auxiliary to the movement of the lymph and chyle is sup-
plied in certain muscular sacs, named lymph-hearts (fig. 100),
and Mr. Wharton Jones has lately shown that the caudal
heart of the eel is a lymph-heart also. The number and
position of these organs vary. In frogs and toads there
are usually four, two anterior and two posterior; in the
frog, the posterior lymph-heart on each side is situated in
the ischiatic region, just beneath the skin; the anterior
lies deeper, just over the transverse process of the third
vertebra. Into each of these cavities several lymphatics
open, the orifices of the vessels being guarded by valves,
which prevent the retrograde passage of the lymph. From
each heart a single vein proceeds and.conveys the lymph
directly into the venous system. In the frog, the inferior
lymphatic heart, on each side, pours its lymph into a

366 ABSORPTION.

branch of the ischiatic vein; by the superior, the lymph
is forced into a branch of the

Fig. too." ' jugular vein, which issues from
its anterior surface, and which
becomes turgid each time that
the sac contracts. Blood is pre-
vented from ‘passing from the
vein into the lymphatic heart by
a valve at its orifice. .

The muscular coat of these
hearts is of variable thickness ;
in some cases it can only be dis-
covered by means of the micro-
scope; but in every case it is composed of transversely-
striated fibres. . The contractions of the hearts are rhyth-
mical, occurring about sixty times in a minute, slowly, and,
in comparison with those of the blood-hearts, feebly.
The pulsations of the cervical pair are not always synchro-
nous with those of the pair in the ischiatic region, and
even the corresponding sacs of opposite sides are not always
synchronous in their action.

Unlike the contractions of the blood-heart, those of the
lymph-heart appear to be directly dependent upon a cer-
tain limited portion of the spinal cord. For Volkmann
found that so long as the portion of spinal cord correspond-
ing to the third vertebra of the frog was uninjured, the
cervical pair of lymphatic hearts continued pulsating after
all the rest of the spinal cord and the brain was destroyed ;
while destruction of this portion, even though all other

* Fig. 100. Lymphatic heart (9 lines long, 4 lines broad) of a large
species of serpent, the Python’ bivittatus (after E. Weber). 4. The
external cellular coat. 5. The thick muscular coat. Four muscular
columns run across its cavity, which communicates with three lympha-
tics (I—only one is seen here), with two veins (2, 2). 6. The smooth
lining membrane of the cavity. 7. A small appendage, or auricle, the
cavity of which is continuous with that of the rest of the organ.

ABSORPTION BY BLOOD-VESSELS. 367

parts of the nervous centres were uninjured, instantly
arrested the heart’s movements. The posterior or ischiatic
pair of lymph-hearts were found to be governed, in like
manner, by the portion of spinal cord corresponding to
the eighth vertebra. Division of the posterior spinal roots
did not arrest the movements; but division of the anterior
roots caused them to cease at once.

Absorption by Blood-vessels.

The process thus named is that which has been com-
monly called absorption by the veins; but the term here
employed seems preferable, since, though the materials
absorbed are commonly found in the veins, this is only
because they are carried into them with the circulating
blood, after being absorbed by all the blood-vessels (but
chiefly by the capillaries) with which they were placed in
contact. There is nothing in the mode of absorption by
blood-vessels, or in the structure of veins, which can make
the latter more active than arteries of the same size, or so
active as the capillaries, in the process.

In the absvrption by the lymphatics or lacteal vessels
just described, there appears something like the exercise
of choice in the materials admitted into them. But the
absorption by blood-vessels presents no such appearance
of selection of materials; rather, it appears that every
substance, whether gaseous, liquid, or a soluble or minutely
divided solid, may be absorbed by the blood-vessels, pro-
vided it is capable of permeating their walls, and of
mixing with the blood; and that of all such substances,
the mode and measure of absorption are determined solely
by their physical or chemical properties and conditions, and
by those of the blood and the walls of the blood-vessels.

The phenomena are, indeed, exactly comparable to that
passage of fluids through membrane, which occurs quite
independently of vital conditions, and the earliest and best
scientific investigation of which was made by Dutrochet.

368 ABSORPTION.

The instrument which he employed in his experiments was
named an endosmometer. It may consist of a graduated
tube expanded into an open-mouthed bell
at one end, over which a portion of mem-
brane is tied (fig. 101). If now the bell be
filled with a solution of a salt—say chloride
of sodium, and be immersed in water, the
water will pass into the solution, and part
of the salt will pass out into the water; the
water will pass into the solution, much more
rapidly than the salt will pass out into the
water, and the diluted solution will rise in
the tube. To this passage of fluids through
membrane the term Osmosis is applied.

The nature of the membrane used as a
septum, and its affinity for the fluids sub-
jected to experiment have an important
influence, as might be anticipated, on the
rapidity and duration of the osmotic current.
Thus, if a piece of ordinary bladder be used
as the septum between water and alcohol, the current is
almost solely from the water to the alcohol, on account of
the much greater affinity of water for this kind of mem-
brane; while, on the other hand, in the case of a membrane
of caoutchoue, the alcohol, from its greater affinity for this
substance, would pass freely into the water.

Fig. ot.

Various opinions have been advanced in regard to the

nature of the force by which fluids of different chemical
composition thus tend to mix through an intervening
membrane. According to some, this power is the result
of the different degrees of capillary attraction exerted by
the pores of the membrane upon the two fluids. Prof.
Graham, however, believes that the passage or osmose of
water through membrane may be explained by supposing
that it combines with the membranous septum, which thus
becomes hydrated, and that on reaching the other side it
partly leaves the membrane, which thus becomes to a

a eee

a

ii

COLLOIDS AND CRYSTALLOIDS. 369

certain degree de-hydrated. For example, a membrane
such as that used in the endosmometer, is hydrated to a
higher degree if placed in pure water than in a neutral
saline solution. Hence, in the case of the endosmometer
filled with the saline solution and placed in water, the
equilibrium of hydration is different on the two sides;
the outer surface being in contact with pure water tends
to hydrate itself in a higher degree than the inner surface
does. ‘‘ When the full hydration of the outer surface ex-
tends through the thickness of the membrane, and reaches
the inner surface, it there receives acheck. The degree of
hydration is lowered, and water must be given up by
the inner layer of the membrane.” Thus the osmose or
current of water through the membrane is caused. The
passage outwards of the saline solution, on the other hand,
is not due, probably, to any actual fluid current; but tola
solution of the salt in successive layers of the water con-
tained in the pores of the membrane, until it reaches the
outer surface and diffuses in the water there situate.

Thus, “ the water movement in osmose is an affair of
hydration anc of de-hydration in the substance of the
membrane or other colloid septum, and the diffusion of the
saline solution placed within the osmometer has litle or
nothing to do with the osmotic result, otherwise than as it
affects the state of hydration of the septum.”

Prof. Graham has classed various substances according
to the degree in which they possess this property of passing, —
when in a state of solution in water, through membrane ;
those which pass freely being termed crystalloids, and those
which pass with difficulty, colloids.

This distinction, however, between colloids and crystal-
loids which is made the basis of their classification, is
by no means the only difference between them. The
colloids, besides the absence of power to assume a crystal-
line form, are characterised by their inertness as acids or
bases, and feebleness in all ordinary chemical relations.

Examples of them are found in albumen, gelatin, starch,
BB

370 ' ABSORPTION.

hydrated alumina, hydrated silicic acid, etc.; while the
crystalloids are characterised by qualities the reverse of
those just mentioned as belonging to colloids. Alcohol,
sugar, and ordinary saline substances are examples of
erystalloids. |

Absorption by blood-vessels is the consequence of their
walls being, like the membranous septum of the endos-
_mometer, porous and capable of imbibing fluids, and of
the blood being so composed that most fluids will mingle
with it. The process of absorption, in an instructive,
though very imperfect degree, may be observed in any
portion of vascular tissue removed from the body. If such
an one be placed in a vessel of water, it will shortly swell,
and become heavier and moister, through the quantity of
water imbibed or soaked into it; and if now, the blood
contained in any of its vessels be let out, it will be found
diluted with water, which has been absorbed by the blood-
vessels and mingled with the blood. The water round the
piece of tissue also will become blood-stained ; and if all
be kept at perfect rest, the stain derived: from the solution
of the colouring matter of the blood (together with which
chemistry would detect some of the albumen and other
parts of the liquor sanguinis) will spread more widely
every day. The same will happen if the piece of tissue be
placed in a saline solution instead of water, or in a solution
of colouring or odorous matter, either of which will give
their tinge or smell to the blood, and receive, in exchange,
the colour of the blood.

Even so simple an experiment will illustrate the ab-
sorption by blood-vessels during life; the process it shows
is imitated, but with these differences: that, during life,
as soon as water or any other substance is admitted into
the blood, it is carried from the place at which it was
absorbed into the general current of the circulation, and
that the colouring matter of the blood is not dissolved so
as to ooze out of the blood-vessels into the fluid which they
are absorbing.

, -
pa ey ae

a ST

:
a
;
:
J
:
‘
,)

RAPIDITY OF ABSORPTION, 371

The absorption of gases by the blood may be thus simply
imitated. If venous blood be suspended in a moist bladder
in the air, its surface will be reddened by the contact of
oxygen, which is first dissolved in the fluid that moistens
the bladder, and is then carried in the fluid to the surface
of the blood: while, on the other hand, watery vapour
and carbonic acid will pass through the membrane, and be
exhaled into the air.

In all these cases alike there is a mutual interchange be-
tween the substances; while the blocd is receiving water,
it is giving out its colouring matter and other constituents :
or, while it is receiving oxygen, it is giving out carbonic
acid and water; so that, at the end of the experiment, the
two substances employed in it are mixed; and if, instead
of a piece of tissue, one had taken a single blood-vessel
full of blood and placed it in the water, both blood and
water would, after a time, have been found both inside and
outside the vessel. In such a case, moreover, if one were
to determine accurately the quantity of water that passed
to the blood, and of blood that passed to the water, it
would be fourd that the former was always greater than
the latter. And so with other substances; it almost always
happens, that if the two liquids placed on opposite sides of
a membrane be of different densities or specific gravities,
a larger quantity of the less dense fluid passes into the
more dense, than of the latter into the former. .

The rapidity with which matters may be absorbed from
the stomach probably by the blood-vessels chiefly, and dif-
fused through the textures of the body, may be gathered
from the history of some experiments by Dr. Bence Jones.
From these it appears that even in a quarter of an hour
after being given on an empty stomach, chloride of lithium
may be diffused into all the vascular textures of the body,

and into some of the non-vascular, as the cartilage of the

hip-joint, as well as into the aqueous humour of the eye,
Into the outer part of the crystalline lens it may pass after

a time, varying from half an hour to an hour and a half.
BB2

372 ABSORPTION.

Carbonate of lithia, when taken in five or ten grain doses
on an empty stomach, may be detected in the urine in 5 or
10 minutes ; or, if the stomach be full at the time of taking
the dose, in 20 minutes. It may sometimes be detected in
the urine, moreover, for six, seven, or even eight days.

Some experiments on the absorption of various mineral
and vegetable poisons, by Mr. Savory, have brought to light
the singular fact, that, in some cases, absorption takes place
more rapidly from the rectum than from the stomach.
Strychnia, for example, when in solution, produces its
poisonous effects much more speedily when introduced into
the rectum than into the stomach. When introduced in
the solid form, however, it is absorbed more rapidly from
the stomach than from the rectum, doubtless because of
the greater solvent property of the secretion of the former
than of that of the latter.

With regard to the degree of absorption by living blood-
vessels, much depends on the facility with which the sub-
stance to be absorbed can penetrate the membrane or tissue
which lies between it and the blood-vessels ; for, naturally,
the blood-vessels are not bare to absorb. Thus absorption
will hardly take place through the epidermis, but is quick
when the epidermis is removed, and the same vessels are
covered with only the surface of the cutis, or with granula-
tions. In general, the absorption through membranes is in
an inverse proportion to the thickness of their epithelia ;
_ so Miller found the urinary bladder of a frog traversed in
less than a second; and the absorption of poisons by the
stomach or lungs appears sometimes accomplished in an
immeasurably small time.

The substance to be absorbed must, as a general rule, be
in the liquid or gaseous state, or, if a solid, must be soluble
in the fluids with which it is brought in contact. Hence

the marks of tattooing, and the discoloration produced by.

nitrate of silver taken internally, remain. Mercury may
be absorbed even in the metallic state; and in that state
may pass into and remain in the blood-vessels, or be

a |

TO EE

——

‘ABSORPTION BY BLOOD-VESSELS. > 373°

deposited from them (Oesterlen) ; and such substances as
exceedingly finely-divided charcoal, when taken into the
alimentary canal, have been found in the mesenteric veins
(Oesterlen) ; the insoluble materials of ointments may also
be rubbed into the blood-vessels; but there are no facts to
determine how these various substances effect their pass-
age. Oil, minutely divided, as in an emulsion, will pass
slowly into blood-vessels, as it will through a filter mois-
tened with water (Vogel); and, without doubt, fatty matters
find their way into the blood-vessels as well as the lymph-
vessels of the intestinal canal, although the latter seem to
be specially intended for their absorption.

As in the experiments before referred to, the less dense
the fluid to be absorbed, the more speedy, as a general
rule, is its absorption by the living blood-vessels. Hence
the rapid absorption of water from the stomach; also of
weak saline solutions; but with strong solutions, there
appears less absorption into, than effusion from, the blood-
vessels.

The absorption is the less rapid the fuller and tenser the
blood-vesselsware ; and the tension may be so great as
to hinder altogether the entrance of more fluid. Thus,
Magendie found that when he injected water into a dog’s
veins to repletion, poison was absorbed very slowly; but
when he diminished the tension of the vessels by bleeding,
the poison acted quickly. So, when cupping-glasses are
placed over a poisoned wound, they retard the absorption
of the poison, not only by diminishing the velocity of the
circulation in the part, but by filling all its vessels too full
to admit more.

On the same ground, absorption is the quicker the more
rapid the circulation of the blood; not because the fluid
to be absorbed is more quickly imbibed into the tissues, or
mingled with the blood, but because as fast as it enters
the blood, it is carried away from the part, and the blood,
being constantly renewed, is constantly as fit as at the first
for the reception of the substance to be absorbed.

374

CHAPTER XI.
NUTRITION AND GROWTH.

Nvrririon or nutritive assimilation is that modification
of the formative process peculiar to living bodies by which
tissues and organs already formed maintain their integrity.
By the incorporation of fresh nutritive principles into their
substance, the loss consequent on the waste and natural
decay of the component particles of the tissues is repaired ;
and each elementary particle seems to have the power not
only of attracting materials from the blood, but of causing
them to assume its structure, and participate in its vital
properties.

The relations between development and growth have
been already stated (Chap. I.); under the head of Nurrt-
Tron will be now considered the process by which parts
are maintained in the same general conditions of form,
size, and composition, which they have already, by develop-
ment and growth, attained; and this, notwithstanding
continual changes in their component particles. It is
by this process that an adult person, in health, is main-
tained, through a series of some years, with the same
general outline of features, the same size and form, and
perhaps even the same weight; although, during all this
time, the several portions of his body are continually
changing: their particles decaying and being removed,
and then replaced by the formation of new ones, which,
in their turn, also die and pass away. Neither is it only
a general similarity of the whole body which is thus main-
tained. Every organ or part of the body, as much as the
whole, exactly maintains its form and composition, as

NUTRITION. 375

the issue of the changes continually taking place among
its particles.

The change of component particles, in which the nutri-
tion of organs consists, is most evidently shown when, in
growth, they maintain their form and other general charac-
ters, but increase in size. When, for example, a long
bone increases in circumference, and in the thickness of
its walls, while, at the same time, its medullary cavity
enlarges, it can only be by the addition of materials to its
exterior, and a coincident removal of them from the
interior of its wall; and so it must be with the growth of
even the minutest portions of a tissue. And that a similar
change of particles takes place, even while parts retain a
perfect uniformity, may be proved, if it can be shown that
all the parts of the body are subject to waste and impair-
ment.

In many parts, the removal of particles is evident.

Thus, as will be shown when speaking of secretion, the

elementary structures composing glands are the parts of
which the secretions are composed: each gland is con-
stantly casting off its cells, or their contents, in the
secretion which it forms: yet each gland maintains its
size and proper composition, because for every cell cast off
a new one is produced. So also the epidermis and all
such tissues are maintained. In the muscles, it seems
nearly certain, that each act of contraction is accompanied
with a change in the composition of the contracting tissue,
although the change from this cause is less rapid and
extensive than was once supposed, Thence, the develop-
ment of heat in acting’ muscles, and thence the discharge
of urea, carbonic acid, and water—the ordinary products
of the decomposition of the animal tissues—which fol-
lows all active muscular exercise. Indeed, the researches
of Helmholtz almost demonstrate the chemical change
that muscles undergo after long-repeated contractions ;
yet the muscles retain their structure and composition,

376 | NUTRITION.
because the particles thus changed are replaced by
new ones resembling those which preceded them. So
again, the increase of alkaline phosphates discharged with
the urine after great mental exertion, seems to prove that
the various acts of the nervous system are attended with
change in the composition of the nervous tissue; yet the’
condition of that tissue is maintained. In short, for every
tissue there is sufficient evidence of impairment in the
discharge of its functions: without such change, the pro-
duction or resistance of physical force is hardly conceivable:
and the proof as well as the purpose of the nutritive pro-
cess appears in the repair or replacement of the changed
particles ; so that, notwithstanding its losses, each tissue
is maintained unchanged.

But besides the impairment and change of composition
to which all parts are subject in the discharge of their
natural functions, an amount of impairment which will be
in direct proportion to their activity, they are all liable to
decay and degeneration of their particles, even while their
natural actions are not called: forth. It may be proved,
as Dr. Carpenter first clearly showed, that every particle
of the body is formed for a certain period of existence in
the ordinary condition of active life; at the end of which
period, if not previously destroyed by outward force or
exercise, it degenerates and is absorbed, or dies and is
cast out.

The simplest examples that can be adduced of this are
in the hair and teeth; and it may be observed, that, in
‘the. process which will now be described, all the great
features of the process of nutrition seem to be re-
presented. *

An eyelash which naturally falls, or which can be drawn

* These and other instances are related more in detail in Mr. Paget’s
Lectures on Surgical Pathology, from which this chapter was originally
written.

My
1

NUTRITION OF HAIR. 377

out without pain, is one that has lived its natural time,
and has died, and been separated from the living parts.
In its bulb such an one will be found different from those
that are still living in
any period of their age.
In the early period of
the growth of a dark
eyelash, the medullary
substance appears like
an interior cylinder of
darker granular sub-
stance, continued down
to the deepest part,
where the hair enlarges
to form the bulb. This
enlargement, which is
of nearly cup-like form,
appears to depend on
the accumulation of
nucleated cells, whose
nuclei, according to
their position, are
either, by narrowing
and elongation, to form the fibrous substance of the outer
part of the growing and further protruding hair, or are to
be transformed into the granular matter of its medullary
portion. At the time of early and most active growth, all
the cells and nuclei contain abundant pigment-matter, and

* Fig. 102, Intended to represent the changes undergone by a hair
towards the close of its period of existence. At A, its activity of growth
is diminishing, as shown by the small quantity of pigment contained in
the cells of the pulp, and by the interrupted line of dark medullary
substance. At B, provision is being made for the formation of a new
hair, by the growth of a new pulp connected with the pulp or capsule
of the old hair. o. A hair at the end of its period of life, deprived of
its sheath and of the mass of cells composing the pulp of a living hair.

378 | NUTRITION.

the whole bulb looks nearly black. The sources of the

material out.of which the cells form themselves are at least
two; the inner surface of the sheath or capsule, which

' dips into the skin, enveloping the hair, and the surface of
a vascular pulp which fits in a conical cavity in the bottom

of the hair-bulb.

Such is the state of parts so long as the growing hair is
all dark. But as the hair approaches the end of its
existence, instead of the almost sudden enlargement at its
* bulb, it only swells a little, and then tapers nearly to a
point; the conical cavity in its base is contracted; and the
cells produced on the inner surface of the capsule contain
no pigment. Still, for some time, it continues thus to live
and grow; and the vigour of the pulp lasts rather longer
than that of the sheath or capsule, for it continues to pro-
duce pigment-matter for the medullary substance of the
hair after the cortical substance has become white. Thus
the column of dark medullary substance appears paler and
more slender, and perhaps interrupted, down to the point
of the conicai-pulp which, though smaller, is still distinct,
because of the pigment-eells covering its surface.

At length the pulp can be no longer discerned, and un-
coloured cells are alone produced, and maintain the latest
growth of the hair. With these it appears to grow yet
some further distance; for traces of the elongation of their
nuclei into fibres appear in lines running from the inner
surface of the capsule inwards and along the surface of the
hair; and the column of dark medullary substance ceases
at some distance above the lower end of the contracted
hair-bulb. The end of all is the complete closure of the
conical cavity in which the hair-pulp was lodged, the
cessation of the production of new cells from the inner
surface of the capsule, and the detachment of the’ hair
which, as a dead part, is separated and falls.

Such is the life of a hair, and such its death; which
death is spontaneous, independent of exercise, or of any

ee NS ee ef ~

_—— = ea

Ks e's?

MAINTENANCE BY NUTRITION. 379

mechanical external force—the natural termination of a
certain period of life, “Yet, before the hair dies, provision
is made for its successor: for when its growth is failing,
there appears below its base a dark spot, the germ or
young pulp of the new hair covered with cells containing
pigment, and often connected by a series of pigment cells
with the old pulp or capsule (fig. 102, 8).

Probably there is an intimate analogy between the pro-
cess of successive life and death, and life communicated to
a successor, which is here shown, and that which constitutes
the ordinary nutrition of a part. It may be objected, that
the death and casting out of the hair cannot be imitated
in internal parts; therefore, for an example in which the
assumed absorption of the worn-out or degenerate internal
particles is imitated in larger organs at the end of their
appointed period of life, the instance of the deciduous or
milk-teeth may be adduced.

Each milk-tooth is develop-
ed from its germ; and in the
course of its own development,
separates a portion of itself to
be the germ of its successor ;
and each, having reached its
perfection, retains for a time
its perfect state, and still
lives, though it does not grow.
But at length, as the new tooth
comes, the deciduous tooth
dies; or rather its crown dies,
and is cast out like the dead hair, while its fang, with
its bony sheathing, and vascular and nervous pulp,’ de-
generates and is absorbed (fig. 103). The degeneration is

Fig. 103.

* Fig. 103. Section of a portion of the upper jaw of achild, showing
anew tooth in process of formation, the fang of the corresponding
deciduous tooth being absorbed.

380 NUTRITION.

accompanied by some unknown spontaneous decomposition
of the fang; for it could not be absorbed unless it was
first so changed as to be soluble. And it is degeneration,
not death, which precedes its removal; for when a tooth-
fang dies, as that of the second tooth does in old age, then
it is not absorbed, but cast out entire, as a dead part.

Such, or generally such, it seems almost certain, is the
process of maintenance by nutrition; the hair and teeth
may be fairly taken as types of what occurs in other parts,
for they are parts of complex organic structure and com-
position, and the teeth-pulps, which are absorbed as well
as the fangs, are very vascular and sensitive.

Nor are they the only instances that might be adduced.
The like development, persistence for a time in the perfect
state, death, and discharge, appear in all the varieties of
cuticles and gland-cells; and in the epidermis, as in the
teeth, there is evidence of decomposition of the old cells, in
the fact of the different influence which acetic acid and
potash exercise on them and on the young cells. Seeing,
then, that the process of nutrition, as thus displayed, both

in active organs and in elementary cells, appears in these
respects similar, the general conclusion may be that, in
nutrition, the ordinary course of each complete elementary
organ in the body, after the attainment of its perfect state
by development and growth, is to remain in that state for
a time; then, independently of the death or decay of the
whole body, and, in some measure, independently of its
own exercise, or exposure to external violence, to die or to
degenerate; and then, being cast out or absorbed, to make
way for its successor.

It appears, moreover, that the length of life which each
part is to enjoy is fixed and determinate, though in some
degree subject to accidents and to the expenditure of life
in exercise. It is not likely that all parts are made to last
a certain and equal time, and then all need to be changed.
The bones, for instance, when once completely formed,

MAINTENANCE BY NUTRITION. 381

must last longer than the muscles and other softer tissues.
But when we see that the life of certain parts is of
determined length, whether they be used or not, we may
assume, from analogy, the same of nearly all. |

Now, the deciduous human teeth have an appointed ©
average duration of life. So have the deciduous teeth of
all other animals; and in all the numerous instances of.
moulting, shedding of antlers, of desquamation, change of _
plumage in birds, and of hair in Mammalia, the only ex-
planation is that these organs have their severally appointed
times of living, at the ends of which they degenerate, die,
are cast away, and in due time are replaced by others
which, in their turn, are to be developed to perfection, to
live their life in the mature state, and in their turn to be
cast off. So also, in some elementary structures we may
discern the same laws of determinate period of life, death,
or degeneration, and replacement. They are evident in the
history of the blood-corpuscles, both in the superseding of
the first set of them by the second at a definite period in
the life of the embryo, and ‘in the replacement of those
that degenerate by others, new-formed from lymph-cor-
puscles (see p. 92). And if we could suppose the blood-
corpuscles grouped together in a tissue instead of floating,
we might have in the changes they present an image of
the nutrition of the elements of the tissues.

The duration of life in each particle is, however, liable to
be modified ; especially by the exercise of the function of
the part. The less a part is exercised the longer do its
component particles appear to live: the more active its
functions are, the less prolonged is the existence of its
individual particles. So in the case of single cells ; if the
general development of the tadpole be retarded by keeping
it in a cold, dark place, and if hereby the function of the
blood-corpuscles be slowly and imperfectly discharged,
they, will maintain their embryonic state for even several
weeks later than usual, the development of the second set

382 NUTRITION.

of corpuscles will be proportionally postponed, and the
individual life of the corpuscles of the first set will es by
the same time, prolonged.

Such being the mode in which the necessity for the pro-
cess of nutritive maintenance is created, such the sources
of impairment and waste of the tissues, the next conside-
ration may be the manner in which the perfect state of a
part is maintained by the insertion of new particles in the
place of those that are absorbed or cast off.

The process by which a new particle is formed in the place
of the old one is probably always a process of develop-
ment; that is, the cell or fibre, or other element of tissue,
passes in its formation through the same stages of develop-
ment as those elements of the same tissue did which were
first formed in the embryo. This is probable from the
analogy of the hair, the teeth, the epidermis, and all the
tissues that can be observed: in all, the process of repair
or replacement is effected through development of the new
parts. The existence of nuclei or cytoblasts in nearly all
parts that are the seats of active nutrition makes the same
probable. For these nuclei, such as are seen so abundant
in strong, active muscles, are not remnants of the embryonic
tissue, but germs or organs of power for new formation,
and their abundance often appears directly proportionate
to the activity of growth. Thus, they are always abundant
in the foetal tissues, and those of the young animal; and
they are peculiarly numerous in the muscles and the brain,
and their disappearance from a part in which they usually
exist is a sure accompaniment and sign of degeneration.

A difference may be drawn between what may be called
nutritive reproduction and nutritive repetition. The former is
shown in the case of the human teeth. As the deciduous
tooth is being developed, a part of its productive capsule
is detached, and serves as a germ for the formation of the
second tooth; in which second tooth, therefore, the first
may be said to be reproduced, in the same sense as that in

NUTRITIVE REPRODUCTION AND REPETITION. 383

which we speak of the organs by which new individuals
are formed, as the reproductive organs. But in the shark’s
jaws, and others, in which we see row after row of teeth
succeeding each other, the row behind is not formed of
germs derived from the row before: the front row is
simply repeated in the second one, the second in the third,
and so on. So, in cuticle, the deepest layer of epidermis-
cells derives no germs from the layer above: their de-
velopment is not like a reproduction of the cells that
have gone on towards the surface before them: it is only
a repetition. It is not improbable that much of the
difference in the degree of repair, of which the several
tissues are capable after injuries or diseases, may be con-
nected with these differences in their ordinary mode of
nutrition.

In order that the process of nutrition may be perfectly
accomplished, certain conditions are necessary. Of these,
the most important are: 1. A right state and composition
of the blood, from which the materials for nutrition are
derived. 2. A regular and not far distant supply of such
blood. 3. A certain influence of the nervous system. 4. A
natural state of the part to be nourished.

I. This right condition of the blood does not necessarily
imply its accordance with any known standard of com-
position, common to all kinds of healthy blood, but rather
the existence of a certain adaptation between the blood
and the tissues, and even the several portions of each
tissue. Such an adaptation, peculiar to each individual, is
determined in its first formation, and is maintained in the
concurrent development and increase of both blood and
tissues; and upon its maintenance in adult life appears to
depend the continuance of a healthy process of nutrition,
or, at least, the preservation of that exact sameness of the
whole body and its parts, which constitutes the perfection
of nutrition. Some notice of the maintenance of this
sameness in the blood has been given already (p. 94), in

384 NUTRITION.

speaking of the power of assimilation which the blood
exercises, a power exactly comparable with this of main-
tenance by nutrition in the tissues. And evidence of the
adaptation between the blood and the tissues, and of the
exceeding fineness of the adjustment by which it is main-
tained, is afforded by the phenomena of diseases, in which,
after the introduction of certain animal poisons, even in
very minute quantities, the whole mass of the blood is
altered in composition, and the solid tissues are perverted
in their nutrition. Itis necessary to refer only to such
diseases as syphilis, small-pox, and .other eruptive fevers,
in illustration. And when the absolute dependence of all the
tissues on the blood for their very existencéd is remembered,
on the one hand, and, on the other, the rapidity with which
substances introduced into the blood are diffused into all,
- even non-vascular textures (p. 371), it need be no source of
wonder that any, even the slightest alteration, from the
normal constitution of the blood, should be immediately
reflected, so to speak, as a change in the nutrition of the
solid tissues and organs which it is destined to nourish.

2. The necessity of an adequate supply of appropriate blood
in or near the part to be nourished, in order that its nutrition
may be perfect, is shown in the frequent examples of
atrophy of parts to which too little blood’ is sent, of morti-
fication or arrested nutrition when the supply of blood is
entirely cut off, and of defective nutrition when the blood

is stagnant in a part. That the nutrition of a part may,

be perfect, it is also necessary that the blood should be
brought sufficiently near to it for the elements of the tissue
to imbibe, through the walls of the’ blood-vessels, the
nutritive materials which they require. The blood-vessels
themselves take no share in the process of nutrition, except
as carriers of the nutritive matter. Therefore, provided
they come so near that this nutritive matter may pass by
imbibition into the part to be nourished, it is compara-
tively immaterial whether they ramify within the substance

CONDITIONS NECESSARY FOR NUTRITION. 385

of the tissue, or are distributed only on its surface or
border, —

The blood-vessels serve alike for the nutrition of the
vascular and the non-vascular parts, the difference between
which, in regard to nutrition, is less than it may seem.
For the vascular, the nutritive fluid is carried in streams
into the interior; for the non-vascular, it flows on the sur-
face; but in both alike, the parts themselves imbibe the
fluid; and although the passage through the walls of the
blood-vessels may effect some change in the materials, yet
all the process of formation is, in both alike, outside the
vessels. Thus, in muscular tissue, the fibrils in the very
centre of the fibre nourish themselves: yet these are dis-
tant from all blood-vessels, and can only by imbibition
receive their nutriment. So, in bones, the spaces between
the blood-vessels are wider than in muscle; yet the parts
in the meshes nourish themselves, imbibing materials from
the nearest source. The non-vascular epidermis, though
no vessels pass into its substance, yet imbibes nutritive
matter from the vessels of the immediately subjacent cutis,
and maintains itself, and grows. The instances of the
cornea and vitreous humour are stronger, yet similar; and
sometimes even the same tissue is in one case vascular, in
the other not, as the osseous tissue, which, when it is in
masses or thick layers, has blood-vessels running into it ;
but when it isin thin layers, as in the lachrymal and tur-
binated bones, has not. These bones subsist on the blood
flowing in the minute vessels of the mucous. membrane,

from which the epithelium derives nutriment on one side,

the bone on the other, and the tissue of the membrane
itself on every side: a striking instance how, from the
same source, many tissues maintain themselves, each exer-
cising its peculiar assimilative and self-formative power.

3. The third condition said to be essential to a healthy
nutrition, is a certain influence of the nervous system.

It has been held that the nervous system cannot be
CC

386 NUTRITION.

essential to a healthy course of nutrition, because in plants
and the early embryo, and in the lowest animals, in which
no nervous system is developed, nutrition goes on without
it.’ But this is no proof that in animals which have a
nervous system, nutrition may be independent of it;
rather, it may be assumed, that in ascending development,
as one system after another is added or increased, so the
highest (and, highest of all, the nervous system) will
always be inserted and blended in a more and more inti-
mate relation with-all the rest: according to the general
law, that the interdependence of parts augments with their
development.

The reasonableness of this assumption is proved by many
facts showing the influence of the nervous system on nutri-
tion, and by the most striking of these facts being observed
in the higher animals, and especially in man. ‘The influ-
ence of the mind in the production, aggravation, and cure
of organic diseases is matter of daily observation, and a
sufficient proof of influence exercised on nutrition through
the nervous system.

Independently of mental influence, injuries either to
portions of the nervous centres, or to individual nerves,
are frequently followed by defective nutrition of the parts
supplied by the injured nerves, or deriving their nervous
influence from the damaged portions of the nervous centres.
Thus, lesions of the spinal cord are sometimes followed by
mortification of portions of the paralysed parts; and this
may take place very quickly, as in a case by Sir B. C.
Brodie, in which the ankle sloughed within twenty-four
hours after an injury of the spine. After such lesions
also, the repair of injuries in the paralysed parts may
take place less completely than in others; so, Mr. Travers
mentions a case in which paraplegia was produced by
fracture of the lumbar vertebree, and, in the same accident,
the humerus and tibia were fractured. The former in due
time united; the latter did not. The same fact was illus-

-
i
4
a
~

“+t

<

:

INFLUENCE OF NERVOUS SYSTEM. 387

trated by some experiments of Dr. Baly, in which having,
in salamanders, cut off the end of the tail, and then thrust
a thin wire some distance up the spinal canal, so as to de-
stroy the cord, he found that the end of the tail was repro-
duced more slowly than in other salamanders in whom the
spinal cord was left uninjured above the point at which
the tail was amputated. Illustrations of the same kind
are furnished by the several cases in which division or
destruction of the trunk of the trigeminal nerve has been
followed by incomplete and morbid nutrition of the corre-
sponding side of the face; ulceration of the cornea being
often directly or indirectly one of the consequences of such
imperfect nutrition. Part of the wasting and slow dege-
neration of tissue in paralysed limbs ‘is probably referable
also to the withdrawal of nervous influence from them;
though, perhaps, more is due to the want of use of the
tissues. |

. Undue irritation of the trunks of nerves, as well as their
division or destruction, is sometimes followed by defective
or morbid nutrition. To this may be referred the cases
in which ulceration of the parts supplied by the irritated
nerves occurs frequently, and continues so long as the
irritation lasts. Further evidence of the influence of the
nervous system upon nutrition is furnished by those cases
in which, from mental anguish, or in severe neuralgic head-
aches, the hair becomes grey very quickly, or even in a few
hours.

So many and various facts leave little doubt that the
nervous system exercises an influence over nutrition as
over other organic processes ; and they cannot be explained
by supposing that the changes in the nutritive processes
are only due to the variations in the size of the blood-
vessels supplying the affected parts.

The question remains, through what class of nerves is
the influence exerted? When defective nutrition occurs in

parts rendered inactive by injury of the motor nerve alone,
cc 2

. 388 NUTRITION.

as in the muscles and other tissues of a paralysed face or —
limb, it may appear as if the atrophy were the direct con- |
sequence of the loss of power in the motor nerves; but it
is more probable that the atrophy is the consequence of
the want of exercise of the parts; for if the muscles be
exercised by artificial irritation of their nerves their nutri- 4
tion will be less defective (J. Reid). The defect of the nutri-
tive process which ensues in the face and other parts,
moreover, in consequence of destruction of the trigeminal
nerve, cannot be referred to loss of influence of any motor.
nerves; for the motor-nerves of the face and eye, as wellas
the olfactory and optic, have no share in the defective nutri-
tion which follows injury of the trigeminal nerve; and one
or all of them may be destroyed without any direct disturb-
ance of the nutrition of the parts they severally supply.

It must be concluded, therefore, that the influence which
is exercised by nerves over the nutrition of parts to which
they are distributed, is to be referred either to those among
their branches which conduct impressions to the brain and
spinal cord, namely, the nerves of common sensation, or,
as it is by some supposed, by nerve-fibres, which preside
specially over the nutrition of the tissues and organs
to which they are supplied. Such special nerves are

called trophic nerves (see Chapter on the Nervous
System).

It is not at present possible to say whether the influence
on nutrition is exercised through the cerebro-spinal or
through the sympathetic nerves, which, in the parts on
which the observation has been made, are generally com-
bined in the same sheath. The truth perhaps is, that it
may be exerted through either or both of these nerves.
The defect of nutrition which ensues after lesion of the
spinal cord alone, the sympathetic nerves being uninjured,
and the general atrophy which sometimes occurs in con-
sequence of diseases of the brain, seem to prove the
influence of the cerebro-spinal system: while the obser-

INFLUENCE OF NERVOUS SYSTEM. 389.

vation of Magendie and Mayer, that inflammation of the
eye is a constant result of ligature of the sympathetic
nerve in the neck, and many other observations of a
similar kind, exhibit very well the influence of the latter
nerve in nutrition.

4. The fourth condition necessary to healthy nutrition is
a healthy state of the part to be nourished. This seems
proved by the very nature of the process, which consists in
the formation of new parts like those already existing; for,
unless the latter are healthy, the former cannot be so.
Whatever be the condition of a part, it is apt to be per-
petuated by assimilating exactly to itself, and endowing
with all its peculiarities the new particles which it forms
to replace those that degenerate. So long as a part is
healthy, and the other conditions of healthy nutrition exist,
it maintains its healthy condition. But, according to the
same law, if the structure of a part be diseased or in any
way altered from its natural condition, the alteration is
maintained; the altered, like the healthy structure, is per-
petuated. .

The same exactness of the assimilation of the new parts
to the old, which is seen in the nutrition of the healthy
tissues, may be observed also in those that are formed in
disease. By it, the exact form and relative size of a
cicatrix are preserved from year to year; by it, the thick-
ening and induration to which imflammation gives rise are
kept up, and the various morbid states of the blood in
struma, syphilis, and other chronic diseases are maintained,
notwithstanding all diversities of diet. By this precision
of the assimilating process, may be explained the law that
certain diseases occur only once in the same person, and
that certain others are apt to recur frequently ; because in
both cases alike, the alteration produced by the first attack
of the disease is maintained by the exact likeness which the
new parts bear to the old ones. 3

The period, however, during which an alteration of

390 NUTRITION.

structure may be exactly maintained by nutrition, is not |
unlimited ; for in nearly all altered parts there appears to ~

exist a tendency to recover the perfect state; and, in many
cases, this state is, in time, attained. To this we may
attribute the possibility of re-vaccination after the lapse of
some years; the occasional recurrence of small-pox, scarlet-
fever, and the like diseases in the same person; the wearing
out of scars, and the complete restoration of tissues that
have been altered by injury or disease.

Such are some of the more important conditions which
appear to be essential to healthy nutrition. Absence or
defect of any one of them is liable to be followed by dis-
arrangement of the process; and the various diseases
resulting from defective nutrition appear to be due to the
failure of these conditions, more often than to imperfection
of the process itself.

GROWTH.

Growth, as has been already observed, consists in the
increase of a part in bulk and weight by the addition to
its substance of particles similar to its own, but more than
sufficient to replace those which it loses by the waste or
natural decay of its tissue. The structure and composi-
tion of the part remain the same; but the increase of
healthy tissue which it receives is attended with the capa-
bility of discharging a larger amount of its ordinary
function.

While development is in progress, growth frequently
proceeds with it in the same part, as in the formation of
the various organs and tissues of the embryo, in which
parts, while they grow larger, are also gradually more
developed until they attain their perfect state. But, com-
monly, growth continues after development is completed,
and in some parts continues even after the full stature
of the body is attained, and after nearly every portion

a

GROWTH. 391

of it has gained its perfect state in both size and composi-
tion.

In certain conditions, this continuance or a renewal of
growth may be observed in nearly every part of the body.
When parts have attained the full size which in the ordi-
nary process of growth they reach, and are then kept in a
moderate exercise of their functions, they commonly (as
already stated) retain almost exactly the same dimensions
through the adult period of life. But when, from any cause,
a part already full-grown in proportion to the rest of the
body, is called upon to discharge an unusual amount of its
ordinary function, the demand is met by a corresponding
“increase or growth of the part. Illustrations of this are
_ afforded by the increased thickening of cuticle at parts
where it is subjected to an unusual degree of occasional
pressure or friction, as in the palms of the hands of persons
employed in rough manual labour; by the enlargement
and increased hardness of muscles that are largely exer-
cised; and by many other facts of a like kind. The
increased power of nutrition put forth in such growth is
greater than might be supposed; for the immediate effect
of increased exercise of a part must be a greater using of
its tissue, and might be expected to entail a permanent
thinning or diminution of the substance of the part. But
_ the energy with which fresh particles are formed is suffi-
cient not only to replace completely those that are worn
away, but to cause an increase in the substance of the
part—the amount of this increase being proportioned to
the more than usual degree in which its functions are
exercised.

The growth of a part from undue exercise of its functions
is always, in itself, a healthy process; and the increased
size which results from it must be distinguished from the
various kinds of enlargement to which the same part may
be subject from disease. In the former case the enlarge-
ment is due to an increased quantity of healthy tissue,

392 NUTRITION. ©

providing more than the previous power to meet a par-
ticular emergency ; the other may be the result of a deposit
of morbid material within the natural structure of the part,
diminishing, instead of augmenting, its fitness for its office.
Such a healthy process of growth in a part, attended with
increased power and activity of its functions, may, however,
occur as the consequence of disease in some other part; in
which case it is commonly called Hypertrophy, i.e., excess
of nutrition. The most familiar examples of this are in
the increased thickness and robustness of the muscular
walls of the cavities of the heart in cases of continued
obstruction to the circulation; and in the increased de-
velopment of the muscular coat of the urinary bladder
when, from any cause, the free discharge of urine from it
is interfered with. In both these cases, though the origin
of the growth is the consequence of disease, yet the growth
itself is natural, and its end is the benefit of the economy ;
it is only common growth renewed or exercised in a part
which had attained its size in due proportion to the rest of
the body.

It may be further mentioned, in relation to the phy-
siology of this subject, that when the increase of function,
which is requisite in the cases from which hypertrophy
results, cannot be efficiently discharged by mere increase
of the ordinary tissue of the part, the development of a
new and higher kind of tissue is frequently combined with
this growth: An example of this is furnished by the
uterus, in the walls of which, when it becomes enlarged
by pregnancy, or by the growth of fibrous tumours, organic
muscular fibres, found in a very ill-developed condition in
its quiescent state, are then enormously developed, and
provide for the expulsion of the foetus or the foreign body.
Other examples of the same kind are furnished by cases in
which, from obstruction to the discharge of their contents
and a consequently increased necessity for propulsive
power, the coats of reservoirs and of ducts become the seat

a ves

ee eee ee ee

a

HYPERTROPHY. 393

of development of organic muscular fibres, which could be
said only just to exist in them before, or were present in a
very imperfectly developed condition.

Respecting the mode and conditions of the process of
growth, it need only be said, that its mode seems to differ
only in degree from that of common maintenance of a part;
more particles are removed from, and many more added to
a growing tissue, than to one which only maintains itself.
But so far as can be ascertained, the mode of removal, the
disposition of the removed parts, and the insertion of the
new particles, are as in simple maintenance.

The conditions also of growth, are the same as those of
common nutrition, and are equally or more necessary to its
occurrence. When they are very favourable or in excess,
growth may occur in the place of common nutrition. Thus
hair may grow profusely in the neighbourhood of old
ulcers, in consequence, apparently, of the excessive supply
of blood to the hair-bulbs and pulps; bones may increase
in length when disease brings much blood to them; and,
cocks’ spurs transplated from their legs into their combs
grow to an unnatural length ; the conditions common to all
these cases being both an increased supply of blood, and
the capability, on the part of the growing tissue, of avail-
ing itself of the opportunity of increased absorption and
nutrition thus afforded to it. In the absence of the last-
named condition, increased supply of blood will not lead
to increased nutrition.

394

CHAPTER XII.
SECRETION.

SECRETION is the process by which materials are sepa-
rated from the blood, and from the organs in which they
are formed, for the purpose either of serving some ulterior
office in the economy, or being discharged from the body
as excrement. In the former case, both the separated
materials and the processes for their separation are termed
secretions ; in the latter, they are named excretions.

Most of the secretions consist of substances which, pro-
bably, do not pre-exist in the same form in the blood, but
require special organs and a process of elaboration for
their formation, e.g., the liver for the formation of bile,
the mammary gland for the formation of milk. The ex-
cretions, on the other hand, commonly or chiefly consist of
substances which, as urea, carbonic acid, and probably
uric acid, exist ready-formed in the blood, and are merely
abstracted therefrom. If from any cause, such as exten-
sive disease or extirpation of an excretory organ, the sepa-
ration of an excretion is prevented, and an accumulation
of it in the blood ensues, it frequently. escapes through
other organs, and may be detected in various fluids of the
body. But this is never the case with secretions ; at least
with those that are most elaborated ; for after the removal
of the special organs by which any of them is elaborated,
it is no longer formed. Cases sometimes occur in which
the secretion continues to be formed by the natural organ,
but not being able to escape towards the exterior, on ac-
count of some obstruction, is re-absorbed into the blood,
and afterwards discharged from it by exudation in other
ways; but these are not instances of true vicarious secre-
tion, and must not be thus regarded.

These circumstances, and their final destination, are,

SEROUS MEMBRANES. . 395

however, the only particulars in which secretions and
excretions can be distinguished ; for, in general, the struc-
ture of the parts engaged in eliminating excretions, ¢.7.,
the kidneys, is as complex, as that of the parts concerned
in the formation of secretions. And since the differences
of the two processes of separation, corresponding with
those in the several purposes and destinations of the fluids,
are not yet ascertained, it will be sufficient to speak in
general terms of the process of separation or secretion.

Every secreting apparatus possesses, as essential parts
of its structure, a simple and apparently textureless mem-
brane, named the primary or basement-membrane ; certain
cells ; and blood-vessels. These three structural elements
are arranged together in various ways; but all the varieties
may be classed under one or other of two principal divi-
sions, namely, membranes and glands.

SECRETING MEMBRANES.

The principal secreting membranes are the serous and
synovial membranes, the mucous membranes, and the
skin.*

The serous membranes are formed of fibro-cellular tissue,
interwoven so as to constitute a membrane, the free surface
of which is covered with a single layer of flattened cells,
forming, in most instances, a simple tesselated epithelium.
Between the epithelium and the subjacent layer of fibro-
cellular tissue, is situated the primary or basement mem-
brane (Bowman).

* The skin will be described in a subsequent chapter.

T Fig. 104. Plan of a secreting membrane : a, membrana propria, or
basement-membrane ; 6, epithelium composed of secreting nucleated
cells; c, layer of capillary blood-vessels (after Sharpey).

396 SECRETION.

In relation to the process of secretion, the layer of fibro-
cellular tissues serves asa ground-work for the ramification
of blood-vessels, lymphatics, and nerves. But in its usual
form:it is absent in some instances, as in the arachnoid
covering the dura mater, and in the interior of the ven-
iricles of the brain. The primary membrane and epithe-
lium are probably always present, and are concerned in
the formation of the fluid by which the free surface of the
membrane is moistened.

The serous membranes are of two principal kinds:
1st. Those which line visceral cavities,—the arachnoid,
pericardium, pleurze, peritoneum, and tunice vaginales.
2nd. The synovial membranes lining the joints, and the
sheaths of tendons and ligaments, with which, also, are
usually included the synovial burs, or burs@ mucosa,
whether these be subcutaneous, or situated beneath ten-
dons that glide over bones.

The serous membranes form closed sacs, and exist
wherever the free surfaces of viscera come into contact
with each other, or lie in cavities unattached to surround-
ing parts. The viscera, which are invested by a serous
membrane, are, as it were, pressed into the shut sac which
it forms, carrying before them a portion of the membrane,
which serves as their investment. To the law that serous
membranes form shut sacs, thereis, in the human subject,
one exception, viz.: the opening of the Fallopian tubes
into the abdominal cavity,—an arrangement which exists
in man and all Vertebrata, with the exception of a few
fishes.

The principal purpose of the serous and synovial mem-
branes is to furnish a smooth, moist surface, to facilitate
the movements of the invested organ, and to prevent the
injurious effects of. friction. This purpose is especially
manifested in joints, in which free and extensive move-
ments take place ; and in the stomach and intestines, which,
from the varying quantity and movements of their contents,

—-

SEROUS MEMBRANES. 397

are in almost constant motion upon one another and the
walls of the abdomen.

The fluid secreted from the free surface of the serous mem-
branes is, in health, rarely more than sufficient to ensure the
maintenance of their moisture. The opposed surfaces of each
serous sac, are at every point in contact with each other, and
leave no space in which fluid can collect. After death, a larger
quantity of fluid is usually found in each serous sac; but this,
if not the product of manifest disease, is probably such as has
transuded after death, or in the last hoursof life. An excess of
such fluid in any of the serous sacs constitutes dropsy of the sac.

The fluid naturally secreted by the serous membranes
appears to be identical, in general and chemical characters,
with the serum of the blood, or with very dilute liquor san-
guinis. It is of a pale yellow or straw-colour, slightly
viscid, alkaline, and, because of the presence of albumen,
coagulable by heat. The presence of a minute quantity

of fibrin, at least in the dropsical fluids effused into the

serous cavities, is shown by their partial coagulation into a
jelly-like mass, on the addition of certain animal substances,
or on mixture with certain fluids, especially such as contain
cells( p. 75 et seg.). This similarity of the serous fluid to
the liquid part of blood, and to the fluid with which most
animal tissues are moistened, renders it probable that it
is, in great measure, separated by simple transudation
through the walls of the blood-vessels. The probability
is increased by the fact that, in jaundice, the fluid in the
serous sacs is, equally with the serum of the blood, coloured
with the bile. But there is reason for supposing that the
fluid of the cerebral ventricles and of the arachnoid sac
are exceptions to this rule; for they differ from the fluids
of the other serous sacs not only in being pellucid,:colour-
less, and of much less specific gravity, but in that they
seldom receive the tinge of bile in the blood, and are not
coloured by madder, or other similar substances introduced
abundantly into the blood.

398 SECRETION.

It is also probable that the formation of synovial fluid
is a process of more genuine and elaborate secretion, by
means of the epithelial cells on the surface of the mem-
brane, and especially of those which are accumulated on
the edges and processes of the synovial fringes; for, in its
peculiar density, viscidity, and abundance of albumen,
synovia differs alike from the serum of blood and from
the fluid of any of the serous cavities.

The mucous membranes line all those passages by which
internal parts communicate with the exterior, and by
which either matters are eliminated from the body or
foreign substances taken into it. They are soft and
velvety, and extremely vascular. Their general structure
resembles that of serous membranes. It consists of
epithelium, basement membrane, and fibro-cellular or
areolar tissue containing blood-vessels, lymphatics, and
nerves. The structure of mucous membranes is less
uniform, especially as regards their epithelium, than that
of serous membranes; but the varieties of structure
in different parts are described in connection with
the organs in which mucous membranes are present,
and need not be here noticed in detail. The external
surfaces of mucous membranes are attached to various
other tissues; in the tongue, for example, to muscle ;
on cartilaginous parts, to perichondrium ; in the cells of
the ethmoid bone, in the frontal and sphenoid sinuses,
as well as in the tympanum, to periosteum; in the
intestinal canal, it is connected with a firm submucous
membrane, which on its exterior gives attachment to the
fibres of the muscular coat.

The mucous membranes are described as lining certain
principal tracts. 1. The digestive tract commences in the
cavity of the mouth, from which prolongations pass into
the ducts of the salivary glands. From the mouth it passes
through the fauces, pharynx, and cesophagus, to the
stomach, and is thence continued along the whole tract of

ke

Lae peat

eS ee

MUCOUS MEMBRANES. | 309

the intestinal canal, to the termination of the rectum, being
in its course arranged in the various folds and depressions
already described, and prolonged .into the ducts of the
pancreas and liver and into the gall-bladder. 2. The
respiratory tract includes the mucous membrane lining the
cavity of the nose, and the various sinuses communicating
with it, the lachrymal canal and sac, the conjunctiva of the
eye and eyelids, and the prolongation which passes along
the Eustachian tubes and lines the tympanum and the
inner surface of the membrana tympani. Crossing the
pharynx, and lining that part of it which is above the soft

palate, the respiratory tract leads into the glottis, whence

it is continued, through the larynx and trachea, to the
bronchi and their divisions, which it lines as far as the
branches of about ,!, of an inch in diameter, and con-
tinuous with it is a layer of delicate epithelial mem-
brane which extends into the pulmonary cells. 3. The
genito-urinary tract, which lines the whole of the -urinary
passages, from their external orifice to the termination
of the tubuli uriniferi of the kidneys, extends into and
through the oigans of generation in both sexes, into the
ducts of the glands connected with them; and in the female
becomes continuous with the serous membrane of the abdo-
men at the fimbriz of the Fallopian tubes.

Along each of the above tracts, and in different portions
of each of them, the mucous membrane presents certain
structural peculiarities adapted to the functions which each
part has to discharge; yet in some essential characters
mucous membrane is the same, from whatever part it is
obtained. In all the principal and larger parts of the several
tracts, it presents, as just remarked, an external layer of

- epithelium, situated upon basement-membrane, and. beneath

this, a stratum of vascular tissue of variable thickness,
which in different cases presents either out-growths in the
form of papillee and villi, or depressions or involutions in the
form of glands. But in the prolongations of the tracts, where

400 SECRETION.

. they pass into gland-ducts, these constituents are reduced
in the finest branches of the ducts to the epithelium, the
primary or basement-membrane, and the capillary blood-
vessels spread over the outer surface of the latter in a
single layer. .

The primary or basement-membrane is a thin trans-
parent layer, simple, homogeneous, and with no discernible
structure, which, on the larger mucous membranes that
have a layer of vascular fibro-cellular tissue, may appear
to be only the blastema or formative substance, out of
which successive layers of epithelium-cells are formed.
But in the minuter divisions of the mucous membranes,
and in the ducts of glands, it is the layer continous and
correspondent with this basement-membrane that forms
the proper walls of the tubes. The cells also which, lining
the larger and coarser mucous membranes, constitute their
epithelium, are continuous with, and often similar to
those which, lining the gland-ducts, are called gland-cells,
rather than epithelium. Indeed, no certain distinction
can be drawn between the epithelium-cells of mucous

membranes and gland-cells. In reference to their position,

as covering surfaces, they might all be called epithelium-
cells, whether they lie on open mucous membranes, or in
gland-ducts; and in reference to the process of secretion,
they might all be called gland-cells, or at least secreting-
cells, since they probably all fulfil a secretory office by
separating certain definite materials from the blood and
from the part on which they are seated. It is only an
artificial distinction which makes them epithelial cells in
one place, and gland-cells in another.

It thus appears, that the tissues essential to the pro-
duction of a secretion are, in their simplest form, a simple
membrane, having on one surface blood-vessels, and on

the other a layer of cells, which may be called either

epithelium-cells or gland-cells. Glands are provided also
with lymphatic vessels and nerves. The distribution of

ae. Se

SECRETING GLANDS. 4OL-

the former is not peculiar, and need not be here con-
sidered. Nerve-fibres are distributed both to the blood-
vessels of the gland and to its ducts; and, in some glands,
it is said, to the secreting cells also.

The structure of the elementary portions of a secreting
apparatus, namely epithelium, ‘simple membrane, and
blood-vessels, having been already described in this and
previous chapters, we may proceed to consider the manner
in which they are arranged to form the varieties of
secreting glands.

SECRETING GLANDS.

The secreting glands are the organs to which the office
of secreting is more especially ascribed : for they appear to
be occupied with it alone. They present, amid manifold
diversities of form and composition, a general plan of
structure, by which they are distinguished from all other
textures of the body; especially, all contain, and appear
constructed with particular regard to the arrangement of,
the cells, which, as already expressed, both line their tubes
or cavities as an epithelium, and elaborate, as secreting
cells, the substances to be discharged from them.

For convenience of description, they may be divided into
three principal groups, the characters of each of which are
determined by the different modes in which the sacculi or
tubes containing the secreting cells are grouped :—

I. The simple tubule, or tubular gland (a, fig. 105), exam-
ples of which are furnished by the several tubular follicles
in mucous membranes: especially by the follicles of Lie-
berkiihn in the mucous membrane of the intestinal canal
(p. 300), and the tubular or gastric glands of the stomach
(p. 268). These appear to be simple tubular depressions of
the mucous membrane on which they open, each consisting
of an elongated gland-vesicle, the wall of which is formed
of primary membrane, and is lined with secreting cells
arranged as an epithelium. To the same class may be

F DD

\

402 SECRETION.

ca

*h

F =

: a an ,

et ee

referred the elongated and tortuous sudoriparous glands of
the skin (p. 426), and the Meibomian follicles beneath the
palpebral conjectiva; though the latter are made more

a
a
<4
4
“

Fig. 105.* ‘

* Fig. 105. Plans of extension of secreting membrane by inversion or
recession in form of cavities. A, simple glands, viz., g, straight tube ;
h, sac; 7, coiled tube. B, multilocular crypts ; 4, of tubular form ;
i, saccular. C, racemose, or saccular compound gland; m, entire
gland, showing branched duct and lobular structure ; 7, a lobule, de-
tached with 0, branch of duct proceeding from it. D, compound

tubular gland (after Sharpey). —

_—

SECRETING GLANDS. 403

complex by the presence of small pouches along their sides
(z, fig. 105), and form a connecting link between the
members of this division and the next, as the former by
their length and tortuosity do between the first division
and the third (p, fig. 105).

2. The aggregated glands, including those that used to be

* called conglomerate, in which a number of vesicles or acini are

arranged in groups or lobules (c, fig. 105). Such are all those
commonly called mucous glands, as those of the trachea,
vagina, and the minute salivary glands. Such, also, are
the lachrymal, the large salivary and mammary: glands,
Brunn’s, Cowper’s, and Duverney’s glands, the pancreas

- and prostate.’ These various organs differ from each other

only in secondary points of structure; such as, chiefly, the
arrangement of their excretory ducts, the grouping of the
acint and lobules, their connection by fibro-cellular tissue,
and supply of blood-vessels. ‘The acini commonly appear
to be formed by a kind of fusion of the walls of several
vesicles, which thus combine to form one cavity lined or
filled with secreting cells which also occupy recesses from
the main cavity. The smallest branches of the gland-ducts
sometimes open into the centres of these cavities; some-
times the acini are clustered round the extremities, or by
the sides of the ducts: but, whatever secondary arrange-
ment there may be, all have the same essential character
of rounded groups of vesicles containing gland-cells, and
opening, either occasionally or permanently, by a common
central cavity into minute ducts, which ducts in the large
glands converge and unite to form larger and larger
branches, and at length, by one common trunk, open on a
free surface of membrane. zs
3. The convoluted tubular glands (p. fig. 105), such as the
kidney and testis, form another division. These consist of
tubules of membrane, lined with secreting cells arranged
like an epithelium. Through nearly the whole of their

long course, the tubules present an almost uniform size and
DD2

*

404 SECRETION,

structure ; ultimately they terminate either in a cul-de-sac,
or by dilating, as in the Malpighian capsules of the kidney,
or by forming a simple loop and returning, as in the

testicle. | |
Among these varieties of structure, all the permanent
glands are alike in some essential points, besides those —
which they have in common with all truly secreting struc-
tures. They agree in presenting a large extent of secreting
surface within a comparatively small space ; in the circum-
stance that while one end of the gland-duct opens on a
free surface, the opposite end is always closed, having
no direct communication with blood-vessels, or any other
canal; and in an uniform arrangement of capillary blood-
vessels, ramifying and forming a network around the walls
and in the interstices of the ducts and acini.

PROCESS OF SECRETION.

From what has been said, it will have already appeared
that the modes in which secretions are produced are at least
two. Some fiuids, such as the secretions of serous mem-
branes, appear to be simply exudations or oozings from the
blood-vessels, whose qualities are determined by those of
the liquor sanguinis, while the quantities are liable to
variation, or are chiefly dependent on the pressure of the
blood on the interior of the blood-vessels. But, in the
production of the other secretions, such as those of mucous
membranes and all glands, other besides these mechanical
forces are in operation. Most of the secretions are indeed
liable to be modified by the circumstances which affect
the simple exudation from the blood-vessels, and the pro-
ducts of such exudations, when excessive, are apt to be
mixed with the more proper products of all the secreting
organs. But the act of secretion in all glands is the result
of the vital processes of cells or nuclei, which, as they
develop themselves and grow, form in their interior the

DISCHARGE OF SECRETIONS. = 805

proper materials of the secretion, and then discharge
them.

The best evidence for this view is: Ist. That cells and
nuclei are constituents of all glands, however diverse their
outer forms and other characters, and are in all glands
placed on the surface or in the cavity whence the secretion
is poured. 2nd. That many secretions which are visible
with the microscope may be seen in the cells of their
glands before they are discharged. Thus, bile may be
often discerned by its yellow tinge in the gland-cells of the
liver; spermatozoids in the cells of the tubules of the
testicles; granules of uric acid in those of the kidneys of
fish ; fatty particles, like those of milk, in the cells of the
mammary gland.

The process of secretion might, therefore, be said to be
accomplished in, and by the life of, these gland-cells.
They appear, like the cells or other elements of any other
organ, to develop themselves, grow, and attain their indi-
vidual perfection by appropriating the nutriment from the
adjacent blood-vessels, and elaborating into the materials
of their walls and the contents of their cavities. In this
perfected state, they subsist for some brief time, and when
that period is over they appear to dissolve or burst and
yield themselves and their contents to the peculiar material
of the secretion. And this appears to be the case in every
part of the gland that contains the appropriate gland-cells ;
therefore not in the extremities of the ducts or in the acini
alone, but in great part of their length.

In these things there is the closest resemblance between
secretion and nutrition; for, if the purpose which the
secreting glands are to serve in the economy be disre-
garded, their formation might be considered as only the
process of nutrition of organs, whose size and other con-
ditions are maintained in, and by means of, the continual
succession of cells developing themselves and passing
away. In other words, glands are maintained by the

406 SECRETION.

development of the cells, and their continuance in the
perfect state: and the secretions are discharged as the
constituent gland-cells degenerate and are set free. The
processes of nutrition and secretion are similar, also, in
their obscurity : there is the same difficulty in saying why,
out of apparently the same materials, the cells of one gland
elaborate the components of bile, while those of another
form the components of milk, and of a third those of saliva,
as there is in determining why one tissue forms cartilage,
another bone, a third muscle, or any other tissue. In
nutrition, also, as in secretion, some elements of tissues,
such as the gelatinous tissues, are different in their
chemical properties from any of the constituents ready-
formed in the blood. Of these differences, also, no
account can be rendered; but, obscure as the cause of
these diversities may be, they are not objections to the
explanation of secretion as a process similar to nutrition ;
an explanation with which all the facts of the case are
reconcilable.

It may be observed that the diversities presented by the
other constituents of glands afford no explanation of the
differences or peculiarities of their several products. There
are many differences in the arrangements of the blood-
_ vessels in different glands and mucous membranes; and,
in accordance with these, much diversity in the rapidity
with which the blood traverses them. But there is no
reason for believing that these things do more than in-
fluence the rate of the process and the quantity of the
material secreted. Cateris paribus, the greater the vascu-
larity of a secreting organ, and the larger the supply of
blood traversing its vessels in a given time, the larger is
the amount of secretion; but there is no evidence that the
quantity or mode of movement of the blood can directly
determine the quality of the secretion.

The Discharge of Secretions from glands may take place
as soon as they are formed; or the secretion may be long

—"—: = - *

DISCHARGE OF SECRETIONS. 407

retained within the gland or its ducts. The secretions of
glands which are continually in active function for the
purification of the blood, such as the kidneys, are generally
discharged from the gland as rapidly as they are formed.
But the secretions of those whose activity of function is
only occasional, such as the testicle, are usually retained
in the ducts during the periods of the gland’s inaction.
And there are glands which are like both these classes,
such as the lachrymal and salivary, which constantly
secrete small portions of fluid, and on occasions of greater
excitement discharge it more abundantly

When discharged into the ducts, the further course of
secretions is effected partly by the pressure from behind ;
the fresh quantities of secretion propelling those that were
formed before. In the larger ducts, its propulsion is
assisted by the contraction of their walls. All the larger
ducts, such as the ureter and common bile-duct, possess in
their coats organic muscular fibres; they contract when
irritated, and sometimes manifest peristaltic movements.
Bernard and Brown-Séquard, indeed, have observed rhyth-
mic contractiuns in the pancreatic and bile-ducts, and
also in the ureters and vasa deferentia. It is probable
that the contractile power extends along the ducts to a
considerable distance within the substance of the glands
whose secretions can be rapidly expelled. Saliva and
milk, for instance, are sometimes ejected with much force ;
doubtless by the energetic and simultaneous contraction of
many of the ducts of their respective glands. The contrac-
tion of the ducts can only expel the fluid they contain
through their main trunk; for at their opposite ends all
the ducts are closed.

Circumstances influencing Secretion.—The influence of
external conditions on the functions of glands, is mani-
fested chiefly in alterations of the quantity of secretion ;
and among the principal of these conditions are variations
in the quantity of blood, in the quantity of the peculiar

408 3 SECRETION.

materials for any secretion that it may contain, and in the
conditions of the nerves of the glands. ,

In general, an increase in the quantity of blood traversing
a gland, coincides with an augmentation of its secretion.
Thus, the mucous membrane of the stomach becomes florid
when, on the introduction of food, its glands begin to
secrete: the mammary gland becomes much more vascular
during lactation; and it appears that all circumstances
which give rise to an increase in the quantity of material
secreted by an organ, produced, coincidently, an increased
supply of blood. In most cases, the increased supply of
blood rather follows than precedes the increase of secre-
tion; as, in the nutritive processes, the increased nutrition
of a part just precedes and determines the increased
supply of blood; but, as also in the nutritive process, an
increased supply of blood may have, for a consequence, an
increased secretion from the glands to which it is sent.

Glands also secrete with increased activity when the
blood contains more than usual of the materials they are
designed to separate. Thus, when an excess of urea is
in the blood, whether from excessive exercise, or from
destruction of one kidney, a healthy kidney will excrete
more than it did before. It will, at the same time, grow
larger: an interesting fact, as proving both that secretion
and nutrition in glands are identical, and that the presence
of certain materials in the blood may lead to the formation
of structures in which they may be incorporated.

The process of secretion is, also, largely influenced by
the condition of the nervous system.

The exact mode in which the nervous system influences
secretion must be still regarded as somewhat obscure. In
part, it exerts its influence by increasing or diminishing the
quantity of blood supplied to the secreting gland, in virtue
of the power which it exercises over the contractility of the
smaller blood-vessels; while it also has a more direct in-
fluence analogous to the trophic influence referred to in the

——

—_—

INFLUENCE OF NERVOUS SYSTEM. 409

chapter on Nurrition. Its influence over secretion, as well
as over other functions of the body, may be excited by
causes acting directly upon the nervous centres, upon the
nerves going to the secreting organ, or upon the nerves of
other parts. In the latter case, a reflex action is produced :
thus the impression produced upon the nervous centres by
the contact of food in the mouth, is reflected upon the
nerves supplying the salivary glands, and produces, through
these, a more abundant secretion of saliva.

Through the nerves, ‘various conditions of the mind also
influence the secretions. Thus, the thought of food may
be sufficient to excite an abundant flow of saliva. And,
probably, it is the mental state which excites the abundant
secretion of urine in hysterical paroxysms, as well as the

-perspirations and, occasionally, diarrhoea, which ensue under

the influence of terror, and the tears excited by sorrow or
excess of joy. The quality of a secretion may also be

affected by the mind; as in the cases in which, through

grief or passion, the secretion of milk is altered, and is,
sometimes so changed as to produce irritation in the
alimentary canal of the child, or even death (Carpenter.)

The secretions of some of the glands seem to bear a
certain relation or antagonism to each other, by which an
increased activity of one is usually followed by diminished
activity of one or more of the others; and a deranged
condition of one is apt’ to entail a disordered state in the
others. Such relations appear to exist among the various
mucous membranes: and the close relation between the |
secretion of the kidney and that of the skin is a subject of
constant observation.

410

CHAPTER XIII.

THE VASCULAR GLANDS; OR GLANDS WITHOUT DUCTS.

Tue materials separated from the blood by the ordinary
process of secretion by glands, are always discharged from
the organ in which they are formed, and either straight-
way expelled from the body, or if they are again received
into the blood, it is only after they have been altered from
their original condition, as in the cases of the saliva and
bile. There appears, however, to be a modification of the
process of secretion, in which certain materials are ab-
stracted from the blood, undergo some change, and are
added to the lymph or restored to the blood, without being
previously discharged from the secreting organ, or made
use of for any secondary purpose. The bodies in which
this modified form of secretion takes place, are usually
described as vascular glands, or glands without ducts, and
include the spleen, the thymus and thyroid glands, the
supra-renal capsules, and, according to (ésterlin and
Ecker and Gull, the pineal gland and pituitary body;
possibly, also the tonsils.

The solitary and agminate glands of the intestine
(p. 302), and lymph-glands in general also closely resem-
ble them; indeed, both in structure and function, the
vascular glands bear a close relation, on the one hand,
to the true secreting glands, and on the other, to the
lymphatic glands. .

The evidence in favour of the view that these organs
exercise a function analogous to that of secreting glands,
has been chiefly obtained from investigations into their
structure, which have shown that most of the glands with-
out ducts contain the same essential structures as the
secreting glands, except the ducts. They are mainly com-

THE DUCTLESS GLANDS. All

_ posed of vesicles, or sacculi, either simple and closed, as in
the thyroid (fig. 106), and supra-renal capsules, or
variously branched, and with the cavities of the several
branches communicating in and by common canals, as in
the thymus (fig. 107). These vesicles, like the acini of
secreting glands, are formed of a delicate homogeneous
membrane, are surrounded with and often traversed by a
vascular plexus, and are filled with finely molecular albu-
minous fluid, suspended in which are either granules of

-

Fig. 106.*

fat, or cytoblasts or nuclei, or nucleated cells, or a mixture
of all these.

Structure of the Spleen.—The spleen is covered exter-
nally almost completely by a serous coat derived from the
peritoneum, while within this is the proper fibrous coat or
capsule of the organ. The latter, composed of connec-
tive tissue, with a large preponderance of elastic fibres,
forms the immediate investment of the spleen. Prolonged
from its inner surface are fibrous processes or trabeculae,

* Fig. 106. Vesicles from the Thyroid Gland of a Child (from Kol-

liker) =°. a, connective tissue between the vesicles ; 6, capsule of the
vesicles ; c, their epithelial lining.

AI2 THE DUCTLESS GLANDS.

which enter the interior of the organ, and, dividing and
anastomosing in all parts, form a kind of supporting
framework or stroma, in the interstices of which the
proper substance of the spleen, or the spleen-pulp, is con-
tained. At the hilus of the spleen, or the part at which -
the blood-vessels, nerves, and lymphatics enter, the fibrous
Fig. 107.* coat is prolonged into the
spleen-substance in the form
of investing sheaths for the
arteries and veins, which
sheaths again are connected
with the trabecule before re-
ferred to.
The spleen-pulp, which is
_ a dark-red or reddish-brown
“ colour, is composed chiefly
of cells. Of these, some are
granular corpuscles resem-
bling the lymph-corpuscles,
both in general appearance
and in being able to perform
amoeboid movements ; others
are red blood-corpuscles of
normal appearance or variously changed; while there arealso
large cells containing either pigment allied to the colouring
matter of the blood, or rounded corpuscles like red blood-cells.
The splenic artery which enters the spleen by its con-
cave surface or hilus divides and subdivides, with but
little anastomosis between its branches, in the midst of the
spleen-pulp, at the same time that its branches are

* Fig. 107. Transverse Section of a Lobule of an Injected Infantile
Thymus Gland (after Kélliker) (magnified 30 diameters). a, capsule
of connective tissue surrounding the lebule; 4, membrane of the
glandular vesicles ; c, cavity of the lobule, from which the larger blood-
vessels are seen to extend towards and ramify in the spheroidal masses
of the lobule.

STRUCTURE OF THE SPLEEN. 413

sheathed, as before said, by the fibrous coat, which they,
so to speak, carry into the spleen with them. Ending in
capillaries, they either communicate, as in other parts of
the body, with the radicles of the veins, or end in lacunar
spaces in the spleen-pulp, from which veins arise (Gray).
On the face of a section of the spleen can be usually

Fig. 108.*

{,

i}

seen, readily with the naked eye, minute, scattered, rounded
or oval whitish spots, mostly from ;}, to ;!, inch in dia-
meter. These are the Malpighian corpuscles of the spleen,
and are situated on the sheaths of the minute splenic
arteries, of which, indeed, they may be said to be out-
growths (fig. 108). For while the sheaths of the larger
arteries are constructed of ordinary connective tissue, this
has become modified where it forms an investment for the

* Fig. 108. The figure shows a portion of asmall artery, to one of the
twigs of which the Malpighian corpuscles are attached.

414 THE DUCTLESS GLANDS.

smaller vessels, so as to be a fine retiform tissue, with
abundance of corpuscles, like lymph-corpuscles contained
in its meshes; and the Malpighian corpuscles are but
small outgrowths of this ecytogenous or cell-bearing con-
nective tissue. ‘They are composed of masses of corpuscles,
intersected in all parts by a delicate fibrillar tissue, which,
though it invests the Malpighian bodies, does not form a
_ complete capsule. Blood-capillaries traverse the Malpi-
ghian corpuscles and form a plexus in their interior. The
structure of a Malpighian corpuscle of the spleen is,
therefore, very similar to that of lymphatic-gland sub-

stance (p. 355).

The general resemblances in structure between certain of
the vascular glands and the true glands lead to the supposi-
tion that both sets of organs pursue, up to a certain point,
a similar course in the discharge of their functions. It
is assumed that certain principles in an inferior state of
organization are effused from the vessels into the sacculi,
and gradually develop into nuclei or cytoblasts, which may
be further developed into cells; that in the growth of these
nuclei and cells, the materials derived from the blood are
elaborated into a higher condition of organization; and
that when liberated by the dissolution of these cells, they
pass into the lymphatics, or are again received into the
blood, whose aptness for nutrition they contribute to
maintain.

The opinion that the vascular glands thus serve for the
higher organization of the blood, is supported by their
being all especially active in the discharge of their functions
during foetal life and childhood, when, for the development
and growth of the body, the most abundant supply of

highly organized blood is necessary. The bulk of the |

thymus gland, in proportion to that.of the body, appears to
bear almost a direct proportion to the activity of the body’s

FUNCTIONS OF DUCTLESS GLANDS. 415

development and growth, and when, at the period of
puberty, the development of the body may be said to be
complete, the gland wastes, and finally disappears. The
thyroid gland and supra-renal capsules, also, though they
probably never cease to discharge some amount of function,
yet are proportionally much smaller in childhood than in
_ footal life and infancy; and with the years advancing to
the adult period, they diminish yet more in proportionate
size and apparent activity of function. The spleen more
nearly retains its proportionate size, and enlarges nearly as
the whole body does.

The function of the vascular vlads seems not essential
to life, at least not in the adult. The thymus wastes and
disappears; no signs of illness attend some of the diseases
which wholly destroy the structure of the thyroid gland;
and the spleen has been often removed in animals, and in
a few instances in men, without any evident ill-consequence.
It is possible that, in such cases, some compensation for
the loss of one of the organs may be afforded by an in-
creased activity of function in those that remain. The
experiment, to be complete, should include the removal of
all these organs, an operation of course not possible without
immediate danger to life. Nor, indeed, would this be
certainly sufficient, since there is reason to suppose that the
duties of the spleen, after its removal, might be performed
by lymphatic glands, between whose structure and that of
the vascular glands there is much resemblance, and which,
it is said, have been found peculiarly enlarged when the
spleen has been removed (Meyer).

Although the functions of all the vascular glands may
be similar, in so far as they may all alike serve for the
elaboration and maintenance of the blood, yet each of them
probably discharges a peculiar office, in relation either to
the whole economy, or to that of some other organ.
Respecting the special office of the thyroid gland, nothing
reasonable can be suggested; nor is there any certain

416 THE DUCTLESS GLANDS.

evidence concerning that of the supra-renal capsules,*
Respecting the thymus gland, the observations of Mr.
Simon, confirmed by those of Friedleben, and others, have
shown that in the hybernating animals, in which it exists
throughout life, as each successive period of hybernation
approaches, the thymus greatly enlarges and becomes laden
with fat, which accumulates in it and in fat-glands connected.
with it, in even larger proportions than it does in the
ordinary seats of adipose tissue. Hence it appears to serve
for the storing up of materials which, being re-absorbed in
inactivity of the hybernating period, may maintain the
respiration and the temperature of the body in the reduced
state to which they fall during that time.

With respect to the office of the spleen, we have
somewhat more definite information. In the first place,
the large size which it gradually acquires towards the ter-
mination of the digestive process, and the great increase
observed about this period in the amount of the finely-
granular albuminous plasma within its parenchyma, and
the subsequent gradual decrease of this material, seem to
indicate that this organ is concerned in elaborating the
albuminous or formative materials of food, and for a time
storing them up, to be gradually introduced into the blood,
according to the demands of the general system. The
small amount of fatty matter in such plasma, leads to the
inference that the gland has little to do in regard to the
preparation of material for the respiratory process.

* Mr. J. Hutchinson, and, more recently, Dr. Wilks, following out
Dr. Addison’s discovery, have, by the collection of a large and valuable
series of cases in which the supra-renal capsules were diseased, demon-
strated most satisfactorily the very close relation subsisting between
disease of these organs and brown discoloration of the skin ; but the
explanation of this relation is still involved in obscurity, and conse-
quently does not aid much in determining the functions of the supra-
renal capsules. )

FUNCTIONS OF SPLEEN. . 417

Then again, it seems not improbable that, as Hewson
originally suggested, the spleen, and perhaps to some
extent the other vascular glands, are, like the lymphatic
glands, engaged in the formation of the germs of subse-
quent blood-corpuscles. For it seems quite certain, that
the blood of the splenic vein contains an unusually large
amount of white corpuscles; and in the disease termed
leucocytheemia, in which the pale corpuscles of the blood
are remarkably increased in number, there is almost
always found an hypertrophied state of the spleen or thy-
roid body, or some of the lymphatic glands. Accordingly

there seems to be a close analogy in function between the
so-called vascular and the lymphatic glands: the former

elaborating albuminous principles, and forming the germs
of new blood-corpuscles out of alimentary materials ab-
sorbed by the blood-vessels; the latter discharging the
like office on nutritive materials taken up by the general

absorbent system. In Kolliker’s opinion, the development
-of colourless and also coloured corpuscles of the blood is

-one of the essential functions of the spleen, into the veins.

of which the new-formed corpuscles pass, and are thus
‘conveyed into the general current of the circulation.

There is reason to believe, too, that in the spleen many
of the red corpuscles of the blood, those probably which
have discharged their office and are worn out, undergo
disintegration ; for in the coloured portion of the spleen-
pulp an abundance of such corpuscles, in various stages of

degeneration, are found, while the red corpuscles in the

splenic venous blood are said to be relatively diminished.
According to Kolliker’s description of this process of dis-
integration, the blood-corpuscles, becoming smaller and
darker, collect together in roundish heaps, which may
remain in this condition, or become each surrounded by a
cell-wall. The cells thus produced may contain from one
to twenty blood-corpuscles in their interior. These cor-
puscles become smaller and smaller; exchange their red

EE

418 THE DUCTLESS GLANDS.

for a golden yellow, brown, or black colour; and, at length,
are converted into pigment-granules, which by degrees
become paler and paler, until all colour is lost. The
corpuscles undergo these changes whether the heaps of
them are enveloped by a cell-wall or not.

Besides these, its supposed direct offices, the spleen is.
believed to fulfil some purpose in regard to the portal
_ circulation, with which it is in close connection. From the
readiness with which it admits of being distended, and
from the fact that it is generally small while gastric
digestion is going on, and enlarges when that act is con-
cluded, it is supposed to act as a kind of vascular reservoir,
or diverticulum to the portal system, or more particularly
to the vessels of the stomach. That it may serve such a
purpose is also made probable by the enlargement which
it undergoes in certain affections of the heart and liver,
attended with obstruction to the passage of blood through
the latter organ, and by its diminution when the congestion
of the portal system is relieved by discharges from the
bowels, or by the effusion of blood into the stomach.
This mechanical influence on the circulation, however,
can hardly be supposed to be more than a very subordinate:
part of the office of an organ of so great complexity as the
spleen, and containing so many other structures besides.
blood-vessels. The same may also be said with regard to
the opinion that the thyroid gland is important as a
diverticulum for the cerebral circulation, or the thymus
for the pulmonary in childhood. These, like the spleen,
must have peculiar and higher, though as yet ill-under-
stood, offices.

419.

CHAPTER XIV.
THE SKIN AND ITS SECRETION.

To complete the consideration of the processes of organic
life, and especially of those which, by separating materials
from the blood, maintain it in the state necessary for the
nutrition of the body, the structure and functions of the
skin must be now considered: for besides the purposes
which it serves—(1I), as an external integument for the |
protection of the deeper tissues, and (2), as a sensitive |
organ in the exercise of touch, it is also (3), an important _
excretory, and (4) an absorbing organ; while it plays a
most important part in (5) theregulation of the tempera- |
- ture of the body, .

Structure of the Skin,

The skin consists, principally, of a layer of vascular
tissue, named the corium, derma, or cutis vera, and an
external covering of epithelium termed the cuticle or
epidermis. Within and beneath the corium are imbedded
several organs with special functions, namely sudoriparous
glands, sebaceous glands, and hair-follicles; and on its sur-
face are sensitive papille. The so-called appendages of
the skin—the hair and nails—are modifications of the
epidermis.

Epidermis.—The epidermis is composed of several layers
of epithelial cells of the squamous kind (p. 30), the deeper
cells, however, being rounded or elongated, and in the
latter instance haying their long axis arranged vertically
as regards the general surface of the skin, while the more

EE 2

420 THE SKIN.

superficial cells are flattened and scaly (fig. 109). The
deeper part of the epider-

Fig. 109.* mis, which is softer and
a more opaque than the su-
perficial, is called the rete
mucosum. Many of the
epidermal cells contain
pigment, and the varying
quantity of this is the
source of the different
shades of tint in the skin,
both of. individuals and
races. The colouring mat-
ter is contained chiefly in
the deeper cells composing
the rete mucosum, and be-
comes less evident in them
as they are gradually
pushed up by those under them, and become, like their
predecessors, flattened and scale-like (fig. 109). It is by
this process of production from beneath, to make up for
the waste at the surface, that the growth of the cuticle is
effected. |
The thickness of the epidermis on different portions of
the skin is directly proportioned to the friction, pressure,
and other sources of injury to which it is exposed; and the
more it is subjected to such injury, within certain limits,
the more does it grow, and the thicker and more horny
does it become; for it serves as well to protect the sen-
sitive and vascular cutis from injury from without, as to
limit the evaporation of fluid from the blood-vessels. The

* Fig. 109. Skin of the negro, in a vertical section, magnified 250
diameters, @, a, cutaneous papille ; 5, undermost and dark coloured
layer of oblong vertical epidermis-cells; ce, mucous or Malpighian
layer ; d, horny layer (from Sharpey).

THE CORIUM OR CUTIS VERA. 421

adaptation of the epidermis to the latter purposes may be
well shown by exposing to the air two dead hands or feet,
of. which one has its epidermis perfect, and the other is
deprived of it; in a day, the skin of the latter will become
brown, dry, and horn-like, while that of the former will
almost retain its natural moisture.

Cutis vera.—The corium or cutis, which rests upon a layer
of adipose and cellular tissue of varying thickness, is a
dense and tough, but yielding and highly elastic structure,
composed of fasciculi of fibro-cellular tissue, interwoven
in all directions, and forming, by their interlacements,
numerous spaces or areole. These areole are large in
the deeper layers of the cutis, and are there usually filled
with little masses of fat (fig. 112): but, in the more super-
ficial parts, they are exceedingly small or entirely oblite-
rated.

By means of its toughness, flexibility, and elasticity, the
. skin is eminently qualified to serve as the general integu-
ment of the body, for defending the internal parts from
external violence, and readily yielding and adapting itself
to their various movements and changes of position. But,
from the abundant supply of sensitive nerve-fibres which
it receives, it is enabled to fulfil a not less important pur-
pose in serving as the principal organ of the sense of
touch. The entire surface of the skin is extremely sen-
sitive, but its tactile properties are due chiefly to the
abundant papillee with which it isstudded. These papille
are conical elevations of the corium, with a single or
divided free extremity, more prominent and more densely
set at some parts than at others (figs. 110 and 111). The
parts on which they are most abundant and most prominent
are the palmar surface of the hands and fingers, and the
soles of the feet—parts, therefore, in which the sense of
touch is most acute. On these parts they are disposed
in double rows, in parallel curved lines, separated from
each other by depressions (fig. 112). Thus they may

~

422 - THE SKIN.

be seen easily on the palm, whereon each raised line is
composed of a double row of papillze, and is intersected by
short transverse lines or furrows corresponding with the
interspaces between the successive pairs of papille. Over
other parts of the skin they are more or less thinly
scattered, and are scarcely elevated above the surface.

Fig. 110.* Fig. 111.F

Their average length is about ~1,th of an inch, and at
their base they measure about =+,,th of an inch in diameter.
Each papilla is abundantly supplied with blood, receiving
from the vascular plexus in the cutis one or more minute
arterial twigs, which divide into capillary loops in its
substance, and then reunite into a minute vein, which
passes out at its base. The abundant supply of blood
which the papille thus receive explains the turgescence or
kind of erection which they undergo when the circulation
through the skin is active. The majority, but not all, of
the papillee contain also one or more terminal nerve-fibres,
from the ultimate ramifications of the cutaneous plexus,
on which their exquisite sensibility depends. The exact
mode in which these nerve-fibres terminate is not yet

* Fig. 110. Papille, as seen with a microscope, on a portion of the
true skin, from which the cuticle has been removed (after Breschet).

+ Fig. 111. Compound papille from the palm of the hand, mag-
nified 60 diameters ; a, basis of a papilla; 0, b, divisions or branches
of the same; ¢, c, branches belonging to papille, of which the bases
are hidden from view (after KGlliker).

TOUCH-CORPUSCLES. 423

satisfactorily determined. In some parts, especially those
in which the sense of touch is highly developed, as for
example, the palm of the hand and the lips, the fibres

Fig. 112.*

----€

appear to terminate, in many of the papille, by one or
more free ends in the substance of a dilated oval-shaped
body, not unlike a Pacinian corpuscle (figs. 136, 137),
occupying the principal part of the interior of the papille,
and termed a touch-corpuscle (fig. 113). The nature of this
body is obscure. Kolliker, Huxley, and others, regard it as

* Fig. 112. Vertical section of the skin and subcutaneous tissue,
from end of the thumb, across tlie ridges and furrows, magnified 20
diameters (from Kolliker) : a, horny, and 0, mucous layer of the epi-
dermis ; ¢, corium; d, panniculus adiposus ; e, papille on the ridges ;
f, fat clusters ; g, sweat-glands ; h, sweat-ducts ; 7, their openings on
the surface.

424 THE SKIN.

little else than a mass of fibrous or connective tissue,

surrounded by elastic fibres, and formed, according to

Huxley, by an increased development of the neurilemma

of the nerve-fibres entering the, papille. Wagner, how-
Fig. 113.*

—

N)
\ \ [\
AN VR ya ay
7 —F
———— ”

ever, to whom seems to belong the merit of first fully
describing these bodies, believes that, instead of thus
consisting of a homogeneous mass of connective tissue,
they are special and peculiar bodies of laminated structure, *
directly concerned in the sense of touch. They do not
occur in all the papillee of the parts where they are found,
and, as arule, in the papille in which they are present
there are no blood-vessels. Since these peculiar bodies in
which the nerve-fibres end are only met with in the papillee
of highly sensitive parts, it may be inferred that they are

* Fig. 113. Papille from the skin of the hand, freed from the cuticle
and exhibiting the tactile corpuscles, Magnified 350 diameters. A.
Simple papilla with four nerve-fibres : a, tactile corpuscle; 6, nerves.

B. Papilla treated with acetic acid: a, cortical layer with cells and
fine elastic filaments; 0, tactile corpuscle with transverse nuclei ; ¢,
entering nerve with neurilemma or perineurium ; d, nerve-fibres wind-
ing round the corpuscle. c. .Papilla viewed from above so as to appear —~
as a cross section: a, cortical layer ; 0, nerve-fibre ; c, sheath of the
tactile corpuscle containing nuclei ; d, core (after Kolliker).

TOUCH-CORPUSCLES; END-BULBS. A28

specially concerned in the sense of touch, yet their absence
from the papillee of Other tactile parts shows that they are

not essential to this sense.

Closely allied in structure to the Pacinian corpuscles
and touch-corpuscles are some little bodies about 51. of

000
an inch in diameter, first particularly described by Krause,

and named by him ‘‘end-bulbs.”” They are generally oval
or spheroidal, and composed externally of a coat of con-
nective tissue enclosing a softer matter, in which the ex-
tremity of a nerve terminates. These bodies have been
found chiefly in the lips, tongue, palate, and the skin of the

glans penis (fig. 114).

Although destined especially for the sense of touch, the
- papille are not so placed as to come into direct contact
with external objects; but, like the rest of the surface of

the skin, are covered by one or more layers of epithelium,

forming the cuticle or . epidermis. The papillz adhere

Fig. 114.* B

}
A\\

ar
As

2 Bat

* Fig. 114. End-bulbs in papille (magnified) treated with acetic
acid. A, from the lips ; the white loops in one of them are capillaries.
B, from the tongue. Two end-bulbs seen in the midst of the simple
papillz : a, a, nerves (from Kolliker). -

|

|

426 | THE SKIN.

very intimately to the cuticle, which is thickest in the
spaces between them, but tolerably level on its outer
surface: hence, when stripped off from the cutis, as after
maceration, its internal surface presents a series of pits
and elevations corresponding to the papille and their

interspaces, of which it thus forms a kind of mould.

Besides affording by its impermeability a check to undue

evaporation from the skin, and providing the sensitive.

cutis with a protecting investment, the cuticle is of service
in relation to the sense of touch. For, by being thickest
in the spaces between the papillae, and only thinly spread
over the summits of these processes, it may serve to sub-
divide the sentient surface of the skin into a number of
isolated points, each of which is capable of receiving a
distinct impression from an external body. By covering
the papillee it renders the sensation produced by external
bodies more obtuse, and in this manner also is subservient
to touch: for unless the very sensitive papillee were thus
defended, the contact of substances would give rise to
pain, instead of the ordinary impressions of touch. This
is shown in the extreme sensitiveness and loss of tactile

power in a part of the skin when deprived of its epidermis,

If the cuticle is very thick, however, as on the heel, touch
becomes imperfect, or is lost, through the inability of the
tactile papillee to receive impressions through the dense
and horny layer covering them.

Sudoriparous Glands.—In the middle of each of the
transverse furrows between the papille, and irregularly
scattered between the bases of the papille in those parts
of the surface of the body in which there are no furrows
between them, are the orifices of ducts of the sudoriparous
or sweat glands, by which it is probable that a large portion
of the aqueous and gaseous materials excreted by the skin

are separated. Each of these glands consists of a small —

lobular mass, which appears formed of a coil of tubular
gland-duct, surrounded by blood-vessels and embedded in

eS ea eS ee er?
\

ae ee

SUDORIPAROUS OR SWEAT GLANDS. — 427

the subcutaneous adipose tissue (fig.* 112), From this
mass, the duct ascends, for a short distance, in a spiral
manner through the deeper part of the cutis, then passing
straight, and then sometimes again becoming spiral, it
passes through the cuticle and opens by an oblique valve-
like aperture. In the parts where the epidermis is thin,
the ducts themselves are thinner and more nearly
straight in their course (fig. 115). The duct, which
maintains nearly the same diameter throughout, is lined
with a layer of epithelium continuous with the epidermis;
while the part which passes through the epidermis is com-
posed of the latter structure only; the cells which imme-
diately form the boundary of the canal in this part being
somewhat differently arranged from those of the adjacent
cuticle.

The sudoriparous glands are abundantly distributed
over the whole surface of the body; but are especially
numerous, as well as very large, in the skin of the palm
of the hand, where, according to Krause, they amount to
2736 in each superficial square inch, and according to
Mr. Erasmus Wilson, to as many as 3528. They are
almost equally abundant and large in the skin of the sole.
The glands by which the peculiar odorous matter of the
axillee is secreted form a nearly complete layer under the
eutis, and are like the ordinary sudoriparous glands, except
in being larger and having very short ducts. In the neck
and back, where they are least numerous, the glands
amount to 417 on the square inch (Krause). ‘Their total
number Krause estimates at 2,381,248; and, supposing
the orifice of each gland to present a surface of ,th of a
line in diameter (and regarding a line as equal to ; th of
an inch), he reckons that the whole of the glands would
present an evaporating surface of about eight square
inches.*

* The peculiar bitter yellow substance secreted by the skin of the
external auditory passage is named cerwmen, and the glands themselves

428 THE SKIN.

Sebaceous Glands.—Besides the perspiration, the skin
Fig. 115.* secretes a peculiar fatty matter, and

| for this purpose is provided with
another set of special organs, termed
sebaceous glands (fig. 115), which, like
the suboriparous glands, are abun-
dantly distributed over most parts of
the body. They are most numerous
in parts largely supplied with hair,
as the scalp and face, and are thickly
distributed about the entrances of the
various passages into the body, as the
anus, nose, lips, and external ear.
They are entirely absent from the
palmar surface of the hands and the
plantar surfaces of the feet. They
are minutely lobulated glands, com-
posed of an aggregate of small vesi-
cles or sacculi filled with opaque
white substances, like soft ointment. Minute capillary
vessels overspread them; and their ducts, which have a
bearded appearance, as if formed of rows of shells, open |
either on the surface of the skin, close to a hair, or, which
is more usual, directly into the follicle of the hair. In
the latter case, there are generally two i to each hair

(fig. 115).

Structure of Hair and Nails.

Hair.—A hair is produced by a peculiar growth and

ceruminous glands ; but they do not much differ in structure from the
ordinary sudoriparous glands.

* Fig. 115. Sebaccous and sudoriparous glands of the skin (after
Gurlt) :—1, the thin cuticle; 2, the cutis; 3, adipose tissue ; 4, a
hair, in its follicle (5); 6, Sebaceous gland, opening into the follicle of
the hair by an efferent duct ; 7, the sudoriparous gland.

STRUCTURE OF HAIR. 429

modification of the epidermis.’ Externally it is covered by
a layer of fine scales closely imbricated, or overlapping
like the tiles of a house, but with the free edges turned
upwards (fig. 116, A). It is called the cuticle of the hair.
Beneath this is a much thicker layer of elongated horny
cells, closely packed together so as to resemble a fibrous
structure. This, very commonly, in the human subj ect,

. occupies the whole of the inside of the hair; but in some

cases there is left a small central space filled by a sub-
stance called the medulla or pith, composed of small collec-
tions of irregularly shaped cells, containing fat- and pig-

ment-granules.

The follicle, in which the root of each hair is contained,
(fig. 117) forms a tubular depression from the surface of the
skin,—descending into the subcutaneous fat, generally to

a greater depth than the sudoriparous glands, and at

its deepest part enlarging in a bulbous form, and often
curving from its previous rectilinear course. It is lined
throughout by cells of epithelium, continuous with those
of the epidermis, and its walls are formed of pellucid
membrane, which commonly, in the follicles of the largest

- hairs, has the structure of vascular fibro-cellular tissue.
At the bottom of the follicle is a small papilla, or projec-

tion of true skin, and it is by the production and out-

* Fig. 116. A, surface of a white hair, magnified 160 diameters. The
wave lines mark the upper or free edges of the cortical scales. B,
separated scales, magnified 350 diameters (after Kolliker).

430 - "THE SKIN.

growth of epidermal cells from the surface of this papilla
that the hair is formed. The inner wall of the follicle is

Fig. 117.* Fig. 118.F

* Fig. 117. Medium-sized hair in its follicle, magnified 50 diameters
(from Kélliker), a, stem cut short ; 0, root ; ¢, knob; d, hair cuticle ;
e, internal, and /, external root-sheath ; g, h, dermic coat of follicle ;
a, papilla ; %, k, ducts of sebaceous glands ; 7, corium ; m, mucous layer —
of epidermis ; 0, upper limit of internal root-sheath (from Kélliker).

+ Fig. 118. Magnified view of the root of a hair (after Kohlrausch). —
a, stem or shaft of hair cut across; 6, inner, and c, outer layer of the ~
epidermal lining of the hair-follicle, called also the inner and outer root- =
sheath ; d, dermal or external coat of the hair-follicle, shown in part,

STRUCTURE OF NAILS. 431

lined by epidermal cells continuous with those covering the
general surface of the skin; as if indeed the follicle had
been formed by a simple thrusting in of the surface of the
integument (figs. 117, 118). This epidermal lining of the
hair-follicle, or root-sheath of the hair, is composed of two
layers, the inner one of which is so moulded on the
imbricated scaly cuticle of the hair, that its inner surface
becomes imbricated also, but of course in the opposite
direction. When a hair is pulled out, the inner layer of
the root-sheath and. part of the outer layer also are com-
monly pulled out with it.

Nails. —A nail, like a hair, is a peculiar arrangement
of epidermal cells, the undermost of which, like those of
the general surface of the integument, are rounded or
elongated, while the superficial are flattened, and of more
horny consistence. That specially modified portion of the
corium, or true skin, by which the nail is secreted, is called —
the matrix.

The back edge of the nail, or the root as it is termed, is
received into a shallow crescentic groove in the matriz,
while the fron+ part is free, and projects beyond the ex-
tremity of the digit. The intermediate portion of the nail
rests by its broad under surface on the front part of the
matrix, which is here called the ded of the nail. This part
of the matrix is not uniformly smooth on the surface, but
is raised in the form of longitudinal and nearly parallel
ridges or laminze, on which are moulded the epidermal
cells of which the nail is made up (fig. 119).

The growth of the nail, like that of a hair, or of the
epidermis generally, is effected by a constant production of
cells from beneath and behind, to take the place of those
which are worn or cut away. Inasmuch, however, as the

e, imbricated scales about to form a cortical layer on the surface of the
hair. . The adjacent cuticle of the root-sheath is not represented, and
the papilla is hidden in the lower part of the knob where that is repre-
sented lighter.

\ 432 THE SKIN.

posterior edge of the nail, from its being lodged in a groove
Fig. 1109.* of the skin, cannot
= grow backwards,
on additions be-
ing made to it, ’
so easily as it
= =. =-6 can pass in the
opposite direc-
tion, any growth
B at its hinder
e part pushes the ‘
whole forwards.
At the same time
fresh cells are
A added to its un-
a der surface, and
thus each portion
@ _ of theenail be-
comes gradually thicker as it moves to the front, until,
projecting beyond the surface of the matrix, it can receive
no fresh addition from beneath, and is simply moved for- |
wards by the growth at its root, to be at last worn away or
cut off. .

ZA NS SA
cylin : Z

(ae
A } LE A; ie y

\\
y

SSS

=
—

——.
2 SISs

Excretion by the Skin.

The skin, as already stated, is the ‘seat of a two-fold
excretion ; of that formed by the sebaceous glands and hair-
follicles, and of the more watery fluid, the sweat or perspira-
tion, eliminated by the sudoriparous glands.

The secretion of the sebaceous glands and hair-follicles

* Fig. 119. Vertical transverse section through a small portion of the
nail and matrix largely magnified (after Kolliker).

A, corium of the nail-bed, raised into ridges or lamine a, fitting in
between corresponding lamine db, of the nail. B, Malpighian, and C,
horny layer of nail: d, deepest and vertical cells ; ¢, upper flattened
cells of Malpighian layer.

a

_ — —————— — oe
‘
‘ .

THE SWEAT. | 433

(for their products cannot be separated) consists of cast-off
epithelium-cells, with nuclei and granules, together with
an oily matter, extractive matter, and stearin; in certain
parts, also, it is mixed with a peculiar odorous principle,
which is said by Dr. Fischer to contain caproic, butyric,
and rutic acids. It is, perhaps, nearly similar in composi-
tion to the unctuous coating, or vernix caseosa, which is
formed on the body of the foetus while in the uterus, and
which contains large quantities both of olein and margarin
(J. Davy). Its purpose seems to be that of keeping the
skin moist and supple, and, by its oily nature, of both
hindering the evaporation from the surface, and guarding
the skin from the effects of the long-continued action of
moisture. But while it thus serves local purposes, its
removal from the body entitles it to be reckoned among
the excretions of the skin; though the share it has in the
purifying of the blood cannot be discerned.

The fluid secreted by the sudoriparous glands is usually

formed so gradually, that the watery portion of it escapes

by evaporation as fast as it reaches the surface. But,
during strong exercise, exposure to great external warmth,
in some diseases, and when evaporation is prevented by the
application of oiled silk or plaster, the secretion becomes
more sensible and collects on the skin in the form of drops
of fluid. A good analysis of the secretion of these glands,
unmixed with other fluids secreted from the skin, can
scarcely be made; for the quantity that can be collected
pure is very small. Krause ina few drops from the palm
of the hand, found an acid reaction, oily matter, and mar-
garin, with water.

The perspiration of the skin, as the term is sometimes
employed in physiology, includes all that portion of the
secretions and exudations from the skin which passes off by
evaporation ; the sweat includes that which may be collected
only in drops of fluid on the surface of the skin. The two

terms are, however, most often used synonymously; and
FF

434 ! THE SKIN.

for distinction, the former is called insensible perspiration :
the latter, sensible perspiration. The fluids are the same,
except that the sweat is commonly mingled with various
substances lying on the surface of the skin. The contents
of the sweat are, in part, matters capable of assuming the —
form of vapour, such as carbonic acid and water, and in
part, other matters which’ are deposited on the skin, and
mixed with the sebaceous secretion. Thenard collected the
perspiration in a flannel shirt which had been washed in
distilled water, and found in it chloride of sodium, acetic
acid, some phosphate of soda, traces of phosphate of lime, and
oxide of iron, together with an animal substance. In sweat
which had run from the forehead in drops, Berzelius found
lactic acid, chloride of sodium, and chloride of ammonium.
Anselmino placed his arm in a glass cylinder, and closed
the opening around it with oiled silk, taking care that the
arm touched the glass at no point. The cutaneous exhala-
tion collected on the interior of the glass, and ran down as
a fluid: on analysing this, he found water, acetate of
ammonia, and carbonic acid; and in the ashes of the dried
residue of sweat he found carbonate, sulphate, and phos-
phate of soda, and some potash, with chloride of sodium,
phosphate and carbonate of lime, and traces of oxide of iron.
Urea has also been shown te be an ordinary constituent of
the fluid of perspiration.

The ordinary constituents of perspiration, may, therefore,
according to Gorup-Besanez, be thus summed up: water,
\fat, acetic, butyric and .formic acid, urea, and salts. The
principal salts are the chlorides of sodium and potassium,
together with, in small quantity, alkaline, and earthy phos-
phates and sulphates; and, lastly, some oxide of iron. Of

these several substances, none, however, need particular
consideration, except the carbonic acid and water.

The quantity of watery vapour excreted from the skin

was estimated very carefully by Lavoisier and Sequin.
The latter chemist enclosed his body in an air-tight bag,

ae

.

EXHALATION FROM THE SKIN. 435

with a mouth-piece. The bag being closed by a strong
band above, and the mouth-piece adjusted and gummed to
the skinaround the mouth, he was weighed, and then re-
mained quiet for several hours, after which time he was
again weighed. The difference in the two weights indi-
cated the amount of loss by pulmonary exhalation. Having
taken off the air-tight dress, he was immediately weighed
again, and a fourth time after a certain interval. The
difference between the two weights last ascertained gave
the amount of the cutaneous and pulmonary exhalation
together ; by subtracting from this the loss by pulmonary
exhalation alone, while he was in the air-tight dress, he
ascertained the amount of cutaneous transpiration. The
repetition of these experiments during a long period,
showed that, during a state of rest, the average loss by
cutaneous and pulmonary exhalation in a minute, is from
seventeen to eightéen grains,—the minimum eleven grains,
the maximum thirty-two grains; and that of the eighteen

grains, eleven pass off by the skin, and seven by the lungs.

The maximum loss by exhalation, cutaneous and pulmo-
nary, in twerty-four hours, is about 331b.; the minimum
about 1;lb. Valentin found the whole quantity lost by
exhalation from the’ cutaneous and respiratory surfaces of
a healthy man who consumed daily 40,000 grains of food
and drink, to be 19,000 grains, or 25lb. Subtracting
from this, for the pulmonary exhalation, 5,000 grains,
and, for the excess 6f the weight of the exhaled carboni’
acid over that of the equal volume of the inspired oxygen,
2,256 grains, the remainder, 11,744 grains, or nearly
1?1b., may represent an average amount of cutaneous
Sshalaiicn, i in the day.

The large quantity of watery vapour thus exhaled from
the skin, will prove that the amount excreted by simple
transudation through the cuticle must be very large, if we
may take Krause’s estimate of about eight square inches

for the total evaporating surface of the sudoriparous
FF2

436 “THE SKIN.

glands; for not more than about 3,365 grains could be
evaporated from such a surface in twenty-four hours,
under the ordinary circumstances in which the surface of
the skin is placed. This estimate is not an improbable
one, for it agrees very closely with that of Milne-Edwards,
who calculated that when the temperature ef the atmo-_
sphere is not above 68° F., the glandular secretion of the
skin contributes only ith to the total sum of cutaneous
exhalation.
i The quantity of watery vapour lost by transpiration, is
of course influenced by all external circumstances which
affect the exhalation from other evaporating surfaces, such
as the temperature, the hygrometric state, and the stillness
of the atmosphere. But, of the variations to which it is
subject under the influence of these conditions, no calcula-
tion has been exactly made. |

Neither, until recently, has there been any estimate of
the quantity of carbonic acid exhaled by the skin on an
average, or in various circumstances. Regnault and Reiset
attempted to supply this defect, and concluded, from some
careful experiments, that the quantity of carbonic acid
exhaled from the skin of a warm-blooded animal is about
= th of that furnished by the pulmonary respiration. Dr.
Edward Smith’s calculation is somewhat less than this.
The cutaneous exhalation is most abundant in the lower
classes of animals, more particularly the naked Am.
phibia, as frogs and toads, whose skin is thin and moist,
and readily permits an interchange of gases between the
blood circulating in it and the surrounding atmosphere.
Bischoff found that, after the lungs of frogs had been tied
and cut out, about a quarter of a cubic inch of carbonic
acid gas was exhaled by the skin in eight hours. And
this quantity is very large, when it is remembered that a
full-sized frog will generate only about half a cubic inch of
carbonic acid by his lungs and skin together in six hours
(Milne-Edwards and Miiller). That the respiratory func-

ABSORPTION BY THE SKIN. 437

tion of the skin is, perhaps, even more considerable in the
higher animals than appears to be the case from the ex-
periments of Regnault and Reiset just alluded to, seemed
probable by the fact observed by Magendie and others,
that if the skin of animals is covered with an impermeable
varnish, or the body enclosed, all but the head, in a
caoutchouc dress, animals soon die, as if asphyxiated;
their heart and lungs being gorged with blood, and their
temperatures, during life, gradually falling many degrees,
and sometimes as much as 36 F. below the ordinary
‘standard (Magendie). Some recent experiments of Lashke-
witzch appear, however, to confirm the opinion of Valentin,
that loss of temperature is the immediate cause of death in
these cases. A varnished animal is said to have suffered
no harm when surrounded by cotton wadding, but it died
when the wadding was removed.

Absorption by the skin has been already mentioned, as an
instance in which that process is most actively accom-
plished. Metallic preparations rubbed into the skin have
the same action as when given internally, only in a less
degree. Mercury applied in this manner exerts its specific
influence upon syphilis, and excites salivation ; potassio-
tartrate of antimony may excite vomiting, or an eruption
extending over the whole body; and arsenic may produce
poisonous effects. Vegetable matters, also, if soluble, or
already in solution, give rise to their peculiar effects, as
cathartics, narcotics, and the like, when rubbed into the
skin. The effect of rubbing is probably to convey the
particles of the matter into the orifices of the glands
whence they are more readily absorbed than they would
be through the epidermis. When simply left in contact
with the skin, substances, unless in a fluid state, are seldom
absorbed.

It has long been a contested question whether the skin
covered with the epidermis has the power of absorbing
water ; and it is a point the more difficult to determine

438 THE SKIN.

because the skin loses water by evaporation. But, from

the result of many experiments, it may now be regarded —

as a well-ascertained fact that such absorption really occurs.
M.-Edwards has proved that the absorption of water by
the surface of the body may take place in the lower
animals very rapidly. Not only frogs, which have a thin
skin, but lizards, in which the cuticle is thicker than in
man, after having lost weight by being kept for some
time in a dry atmosphere, were found to recover both their
weight and plumpness very rapidly when immersed in
water. When merely the tail, posterior extremities, and
posterior part of the body of the lizard were immersed, the
water absorbed was distributed throughout the system.
And a like absorption through the skin, though to a less
xtent, may take place also in man.

Dr. Madden, having ascertained the loss of weight, by
cutaneous and pulmonary transpiration, that occurred
during half an hour in the air, entered the bath, and
remained immersed during the same period of time, breath-
ing through a tube which communicated with the air
exterior to the room. He was then carefully dried and
again weighed. Twelve experiments were performed in
this manner; and in ten there was a gain of weight,
varying from 2 scruples to 5 drachms and 4 scruples, or a
mean gain of I drachm 2 scruples and 13 grains. The
loss in the air during the same length of time (half an
hour) varied in ten experiments from 2} drachms to
I ounce 2} scruples, or in the mean was about 63 drachms.
So that, admitting the supposition that the cutaneous
transpiration was entirely suspended, and estimating the
loss by pulmonary exhalation at 3 drachms, there was, in
these ten experiments of Dr. Madden, an average absorp-
tion of 4 drachms, 1 scruple, and 3 grains, by the surface
of the body, during half an hour. In four experiments
performed by M. Berthold, the gain in weight was spi
than in those of Dr. Madden. '

ae a

ABSORPTION BY THE SKIN. 439

-

In severe cases of dysphagia, when not even fluids can
be taken into the stomach, immersion in a bath of warm
water or of milk and water may assuage the thirst ; and-it
has been found in such cases that the weight of the body
is increased by the immersion. Sailors also, when destitute
of fresh water, find their urgent thirst allayed by soaking
their clothes in salt water and wearing them in that state
but these effects may be in part due to the hindrance to
the evaporation of water from the skin.

The absorption, also, of different kinds of gas by the
skin is proved by the experiments of Abernethy, Cruik-
shank, Beddoes, and others. In these cases, of course,
the absorbed gases combine with the fluids, and lose the
gaseous form. Several physiologists have observed an
absorption of nitrogen by the skin. Beddoes says, that he -
saw the arm of a negro become pale for'a short time when
immersed in chlorine; and Abernethy observed that when
_ he held his hands in oxygen, nitrogen, carbonic acid, and
other gases contained in jars, over mercury, the volume of
the gases became considerably diminished.

The share which the evaporation from the skin has in
the maintenance of the uniform temperature of the body,
and the necessary adaptation thereto of the production of
heat, have been already mentioned (p. 239). ,

440

CHAPTER XV.

THE KIDNEYS AND THEIR SECRETION.
Structure of the Kidneys.

Tue kidney is covered on the outside by a rather tough
fibrous capsule, which is slightly attached by its inner sur-
face to the proper substance of the organ by means of very
fine fibres of areolar tissue and. minute blood-vessels.

From the healthy kidney, therefore, it may be easily torn

off without injury to the subjacent cortical portion of the
organ. At the hilus or
notch of the kidney, it
becomes continuous with
the external coat of the
upper and dilated part of
the ureter.

length-wise through the
part of its substance is

seen to be composed of
two chief portions, called

RN. = respectively the cortical

Ja He = and the medullary portion,

“i “My, i ws the latter being also some-
>

times called the pyramidal
portion, from the fact of its being composed of about a

* Fig. 120, Plan of a longitudinal section through the pelvis and
substance of the right kidney, 4; a, the cortical substance; 6, b, broad
part of the pyramids of Malpighi ; c, c, the divisions of the pelvis
named calyces, laid open ; ¢’, one of these unopened ; d, summit of the

pyramids or papille projecting into calyces ; ¢, ¢, section of the narrow ~

part of two pyramids near the calyces ; », pelvis or enlarged divisions of
the ureter within the kidney ; ~, the ureter ; s, the sinus; /, the hilus,

On making a_ section

kidney (fig. 120) the main.

STRUCTURE OF THE KIDNEY. 441

dozen conical bundles of urine-tubes, each bundle being
called a pyramid. The upper part of the duct of the
organ, or the ureter, is dilated into what is called the pelvis
of the kidney; and this, again, after separating into two
or three principal divisions, is finally subdivided into still
smaller portions, varying in number from about 8 to 12,
or even more, and called calyces. Each of these little
calyces or cups, again, receives the pointed extremity or
papilla of a pyramid. Sometimes, however, more than one
papilla is received by a caly«.

The kidney is a gland of the class called éibolae. and
both its cortical and medullary portions are composed
essentially of secreting tubes, the tubuli wriniferi, which
by one extremity, in the cortical Fig. 121.*
portion, end commonly in little
saccules containing blood-ves-
sels, called Malpighian bodies,
and by the other open through
the papille into the pelvis of the
kidney, and thus discharge the
urine which flows through them.

In the pyramids they are
chiefly straight—dividing and
diverging as they ascend through
these into the cortical portion ;
while in the latter region they
spread out more irregularly, and
become much branched and convoluted.

The tubuli uriniferi (fig. 121) are composed of a nearly
homogeneous membrane, lined internally by spheroidal
epithelium, and for the greater part of their extent are
about ;1, of an inch in diameter,—becoming somewhat

~

* Fig. 121. A. Portion of a secreting canal from the cortical sub-
stance of the kidney. 3. The epithelium or gland-cells, more highly
magnified (700 times).

442 THE KIDNEYS AND THEIR SECRETION,

larger than this immediately before they open through the
‘ Pig. 122.* papille. On tracing these tu-
SUS OT SU Ree Ae bules upwards from the papillz,
they are found to divide dicho-

if } Q tomously as they ascend through
the pyramids, and on reaching

the bases of the latter, they
begin to branch and diverge

' more widely, and to form by —
their branches and convolutions
the essential part of the cortical
portion of the organ. At their
extremities they become dilated
into the Malpighian capsules.
Until recently, it was believed
that the straight tubules in the
pyramids branch out and be-
come convoluted immediately on
reaching the bases of the pyra-
mids ; but between the straight
tubes in the pyramids and the
\) | convoluted tubes in the cortical
portion, there has been shown to

be 4 system of tubules of smaller diameter than éither,
which form intercommunications between the two varieties
formerly recognised. These intervening tubules, called the
looped tubes of Henle, arising from the straight tubes in

* Fig. 122. Diagram of the looped uriniferous tubes and their con-
nection with the capsules of the glomeruli (from Southey, after Ludwig).
In the lower part of the figure one of the large branching tubes is shown
opening on a papilla ; in the middle part two of the looped small tubes
are seen descending to form their loops, and re-ascending in the medul-
lary substance ; while in the upper or cortical part, these tubes, after
some enlatpéniont; are represented as becoming convoluted an ilated
in the capsules of glomeruli.

STRUCTURE OF THE KIDNEY. 443

some part of their course, or being continued from their
extremities at the bases of the pyramids, pass down loop-
wise in the pyramids for a longer or shorter distance, and
then, again turning up, end in the convoluted tubes whose
extremities are dilated into the Malpighian capsules before
referred to (fig. 122). On a transverse section of a pyramid
(fig. 123), these looped tubes are seen to be of much
smaller calibre than the straight ones, which are passing
: - down to open through the papillee.
| The Malpighian bodies are found only in the cortical part.
; of the kidney. On a section of the organ, some of them
: are just visible to the naked eye as minute red points;
others are too small to be thus seen. Their average
diameter is about =4, of an inch. Each of them is com-
posed of the dilated extremity of an urinary tube, or
Malpighian capsule, enclosing a tuft of blood-vessels.

In connection |
with these little
bodies the gene-
ral distribution of ,

- blood-vessels" to #4
the kidney may be
here considered. ~7

The renal ar-

-tery divides into
several branches,
which, passing in
at the hilus of
the kidney, and
covered by a fine
sheath of areolar | |

: tissue derived from the capsule, enter the substance of the

Fig. 123.*

seeiey sates!

* Fig. 123. Transverse section of a renal papilla (from Kolliker) *°,
a, larger tubes or papillary ducts ; b, smaller tubes of Henle ; ¢, blood-
vessels, distinguished by their flatter epithelium; d, nuclei of the
stroma.

444. THE KIDNEYS AND THEIR SECRETION. +

organ chiefly in the intervals between the papillew, and x

penetrate the cortical substance, where. this 3 dips down
< between the bases of the e pyramids. Here they form a.
| tolerably dense plexus of an arched form, and from this

are given off smaller arteries which ultimately supply the :

Malpighian bodies. a

Fig. 124.* The small afferent artery (fig. ‘2
= 124), which enters the Malpi-
ghian body by perforating the
capsule, breaks up in the interior
into a dense and convoluted and
looped capillary plexus, which is
ultimately gathered up again
into a single small efferent vessel,
comparable to a minute vein,
which leaves the Malpighian
capsule just by the point at
which the afferent artery enters it. On leaving, it does
not immediately join other small veins as might have been |
expected, but again breaking up into a network of capil-
lary vessels, is distributed on the exterior of the tubule,
from whose dilated end it had just emerged. After this
second breaking up it is finally collected into a small vein,
which, by union with others like it, helps to form the
radicles of the renal vein.

The Malpighian capsule is lined by a layer of fine squa-
mous epithelial cells; but whether the small glomerulus
or tuft of capillaries in the interior is covered by a similar
layer is uncertain. Kolliker believes that such a covering,

* Fig. 124. Diagram showing the relation of the Malpighian body
to the uriniferous ducts and blood-vessels (after Bowman) : a, one of
the interlobular arteries ; a’, afferent artery passing intothe glomerulus; . ;
c, capsule of the Malpighian body, forming the termination of and con-
tinuous with ¢, the uriniferous tube ; ¢’, e’, efferent vessels which sub-
divide in the plexus p, surrounding the tube, and finally terminate in
the branch of the renal vein e¢.

X @2L hen ‘Lic f% Af Ss bb t YG wet hoe e
OG isco td Matas :

STRUCTURE OF THE KIDNEY. 445

although exceedingly thin, is present, and has delineated
the appearance in the accompanying diagram (fig. 125).

Besides the small afferent arteries of the Malpighian
bodies, there are, of course, Fig. 125.*
others which are distri- 30
buted in the ordinary
manner, for nutrition’s
sake, to the different parts
of the organ; and in the
pyramids, between the
tubes, there are numerous
straight vessels, the vasa
recta, supposed by some
observers to be branches
of vasa efferentia from
Malpighian bodies, and
therefore comparable to the
venous plexus around the tubules in the cor aie portion,
while others think that they arise directly from small
branches of the renal arteries.

Between th» tubes, vessels, etc., which make up the
main substance of the kidney, there exists in small quantity
a fine matrix of areolar tissue.

The nerves of the kidney are derived from the renal
plexus. +

* Fig. 125. Semidiagrammatic representation of a Malpighian body
in its relation to the uriniferous tube (from Kolliker) *$°. a, capsule
of the Malpighian body ; d, epithelium of the uriniferous tube ; e, de-
tached epithelium ; /, afferent vessel ; g, efferent vessel ; , convoluted
vessels of the glomerulus.

+ For a more detailed account of the structure of the kidney and a
summary of the various opinions on the subject, the student may be
referred especially to Quain’s Anatomy, 7th ed., and to a paper by ~
Dr. Reginald Southey in vol. i. of the St. Bartholomew’s Hospital
Reports.

r

446 THE KIDNEYS AND THEIR SECRETION. ~

Secretion of Urine.

The separation from the blood of the solids in a state
of solution in the urine is probably effected, like other
secretions, by the agency of the gland-cells, and equally
in all parts of the urine-tubes. The urea and uric acid,
and perhaps some of the other constituents existing ready
formed in the blood, may need only separation, that is
they may pass from the blood to the urine without further
elaboration; but this is not the case with some of the
other principles of the urine, such as the acid phosphates
and the sulphates, for these salts do not exist as such in
the blood, and must be formed by the chemical agency of
the cells. .

The watery part of the urine is probably in part sepa-
rated by the same structures that secrete the solids, but
the ingenious suggestion of Mr. Bowman that the water
of the urine is mainly strained off, so to speak, by the
Malpighian bodies, from the blood which circulates in their
capillary tufts, is exceedingly probable; although if, as
Kélliker and others maintain, there is an epithelial cover-
ing to these tufts or glomeruli, it is very likely that the
solids of the urine may be in part secreted here also. We
may, therefore, conclude that all parts of the tubular
system of the kidney take part in the secretion of the
urine asa whole, but that there is a provision also in the
arrangement of the vessels in the Malpighian bodies for a
more simple draining off of water from the blood when
required.

The large size of the renal arteries and veins permits so
rapid a transit of the blood through the kidneys, that the
whole of the blood is purified by them. The secretion of
urine is rapid in comparison with other secretions, and as
each portion is secreted, it propels that which is already in
the tubes orwards into the pelvis of the kidney. Thence
through the ureter the urine passes into the bladder, into

\=

PASSAGE OF URINE INTO THE BLADDER. 447

which its rate and mode of entrance has been watched in

cases of ectopia vesice, t.¢., of such fissures in the anterior
and lower part of the walls of the abdomen, and of the
front wall of the bladder, as exposed to view its hinder wall
together with the orifices of the ureters. Some good
observations on such cases were made by Mr. Erichsen.
The urine does not enter the bladder at any regular rate,
nor is there a synchronism in its movement through the
two ureters. During fasting, two or three drops enter the
bladder every minute, each drop as it enters first raising
up the little papilla on which, in these cases, the ureter
opens, and then passing slowly through its orifice, which
at once again closes like a sphincter. In the recumbent
posture, the urine collects for a little time in the ureters,
then flows gently, and, if the body be raised, runs from
them in a stream till they are empty. Its flow is increased
in deep inspiration, or straining, and in active exercise, and
in fifteen or twenty minutes after a meal.

The same observations, also, showed how fast some
substances pass from the stomach through the circulation,
and through +he vessels of the kidneys. Ferrocyanide of
potassium so passed on one occasion in a minute: vegetable
substances, such as rhubarb, occupied from sixteen to
thirty-five minutes; neutral alkaline salts with vegetable
acids, which were generally decomposed in transitu, made
the urine alkaline in from twenty-eight to forty-seven
minutes. But the times of passage varied much; and the
transit was always slow when the substances were taken
during digestion.

The urine collecting in the urinary bladder is prevented
from regurgitation into the ureters by the mode in which
these pass through the walls of the bladder, namely; by
their lying for between half and three-quarters of an inch
between the muscular and mucous coats, and then turning
rather abruptly forwards, and opening through the latter,
it collects till the distension of the bladder is felt either
by direct sensation, or, in ordinary cases, by a transferred

448 THE URINE.

sensation at and near the orifice of the urethra. Then, the
effort of the will being directed primarily to the muscles of
the abdomen, and through them (by reason of its tendency
to act with them) to the urinary bladder, the latter,
though its muscular walls are really composed of inyo-
luntary muscle, contracts, and expels the urine. (See also

p. 223.)
The Urine: its general Properties.

Healthy urine is a clear limpid fluid, of a pale yellow or
amber colour, with a peculiar faint.aromatic odour, which
becomes pungent and ammoniacal when decomposition
takes place. The urine, though usually clear and trans-
parent at first, often becomes as it cools opaque and
turbid from the deposition of part of its constituents pre-
viously held in.solution ; and this may be consistent with
health, though it is only in disease that, in the tempera-
ture of 98° or 100°, at which it is voided, the urine is
turbid even when first expelled. Although ordinarily of
pale amber colour, yet, consistently with health, the urine
may be nearly colourless, or of a brownish or deep orange
tint, and, between these extremes, it may present every
shade of colour.

When secreted, and most commonly when first voided,
the urine has a distinctly acid reaction in man and all car-
nivorous animals, and it thus remains till it is neutralized
or made alkaline by the ammonia developed in it by
decomposition. In most herbivorous animals, on the con-
trary, the urine is alkaline and turbid. The différence
depends, not on any peculiarity in the mode of secretion,
but on the differences in the food on which the two classes
subsist: for when carnivorous animals, such as dogs, are
restricted to a vegetable diet, their urine becomes pale,
turbid, and alkaline, like that of an herbivorous animal,
but resumes its former acidity on the return to an animal
diet; while the urine voided by herbivorous animals, ¢.g.,
rabbits, fed for some time exclusively upon animal sub-

SPECIFIC GRAVITY OF URINE, 449

stances, presents the acid reaction and other qualities of
the urine of Carnivora, its ordinary alkalinity, being re-
stored only on the substitution of a vegetable for the animal
diet (Bernard). Human urine is not usually rendered
alkaline by vegetable diet, but it becomes so after the free
use of alkaline medicines, or of the alkaline salts with car-
bonic or vegetable acids; for these latter are changed into
alkaline carbonates previous to elimination by the kidneys.
Except in these cases, it is very rarely alkaline, unless
ammonia has been developed in it by decomposition com-
mencing before it is evacuated from the bladder.

The average specific gravity of the human urine is about
1020. Probably no other animal fluid presents so many -
varieties in density within twenty-four hours as the urine
does; for the relative quantity of water and of solid
constituents of which it is composed is materially influ-
enced by the condition and occupation of the body during
the time at which it is secreted, by the length of time
which has elapsed since the last meal, and by several
other accidental circumstances. The existence of these
causes of difference in the composition of the urine has.
led to the secretion being described under the three
heads of urina sanguinis, wrina potus, and urina cibi. The
first of these names signifies the urine, or that part of it
which is secreted from the blood at times in which neither
food nor drink has been recently taken, and is applied
especially to the urine which is evacuated in the morning
before breakfast. The urina potus indicates the urine
secreted shortly after the introduction of any considerable
quantity of fluid into the body: and the wrina cibi the por-
tions secreted during the period immediately succeeding a
meal of solid food. The last kind contains a larger quantity
of solid matter than either of the others; the first or
second, being largely diluted with water, possesses a com-
paratively low specific gravity. Of these three kinds, the
morning urine is the best calculated for analysis, since it

represents the simple secretion unmixed with the elements
GG

450 THE URINE.

of food or drink; if it be not used, the whole of the urine
passed during a period of twenty-four hours should be
taken. In accordance with the various circumstances
above mentioned, the specific gravity of the urine may,
consistently with health, range widely on both sides of
the usual average. The average healthy range may
be stated at from 1015 in the winter to 1025 in the
summer, and variations of diet and exercise may make as
great a difference. In disease, the variation may be
greater ; sometimes descending, in albuminuria, to 1004,
and frequently ascending in diabetes, when the urine is
loaded with sugar, to 1050, or even to 1060.

The whole quantity of urine secreted in twenty-four
hours is subject to variation according to the amount of
fluid drunk, and the proportion of the latter passing off
from the skin, lungs, and alimentary canal. It is because
the secretion of the skin is more active in summer than in
winter, that the quantity of urine is smaller, and its

specific gravity proportionately higher. On taking the |

mean of numerous observations by several experimenters,
Dr. Parkes found that the average quantity voided in
twenty-four hours by healthy male adults from twenty to

forty years of age, amounted to 52} fluid ounces.

_—_—,
Chemical Composition of the Urine.

The urine consists of water, holding in solution certain
animal and saline matters as its ordinary constituents, and
occasionally various matters taken into the stomach as
food—salts, colouring matter, and the like. The quan-
tities of the several natural and constant ingredients of
the urine are stated somewhat differently by the different
chemists who have analysed it; but many of the differences
are not important, and the well-known accuracy of the
several chemists renders it almost immaterial which of the
analyses is adopted. The analysis by A. Becquerel being
adopted by Dr. Prout, and by Dr. Golding Bird, will be
here employed. (Table I.)

COMPOSITION OF URINE. ASI

Table II. has been compiled from the observations of
Dr. Parkes, and of numerous other authors quoted in his
admirable work on the urine.

Taste I. ;
Average quantity of each constituent of the Urine in
1000 parts.
Water. Pg , ; ; ‘ = : . + 967°
Urea. : é : : q - - ‘ ; - 14°230
Urié acid... ; ‘ , : : 2 9 e% 468
Colouring matter . } . + ) inseparable from :
10°167
Mucus, and animal etipnatiin matter f each other
Sulphates | =e oe
Lime
Bi-phosphates se ee
Salts Ragraatia : : : : 8°135
. { Sodium
peor ) Potassium
Hippurate of soda
Fluoride of potassium /
Silica . : ; ; : ‘ ; ‘ ? , . traces.
1000°000
TasiE II.

Average quanti y of the chief constituents of the Urine excreted
in 24 hours Ve healthy male adults.

Water... : d j ; 4 : 52° fluid ounces.
Urea . ‘ - ‘ : F : . . 512°4 grains.
Uric acid ‘ 5 : ; ? Soy am
Hippuric acid, uncertain, pr Siabty 10 to 15° a
Sulphuric acid. 2 : : ‘ eal anit oy
Phosphoric acid. a ee : : , 45° »
Chlorine . . , ‘ J) tare WIOSO & 155
Chloride of FRE 2 : = 7 : San ‘ss
Potash. F ; j $ y , She 53° ”
Soda F - 2 é 2 % : 125° ”
Lime . : ‘ : ‘ : ; My c's ee
Magnesia e ‘ - e . . . . ” 2”?
Mucus 2 e ° 2 . * . . ? ”?

‘ Creatin

Creatinin
Extractives Pigment

| Xanthin ) J Z aia E50 55

Hypoxanthin
Resinous matter,
etc. Ga 2

452 THE URINE.

From these proportions, however, most of the consti-
tuents are, even in health, liable to variations. Especially
the water is so. Its variations in different seasons, and
according to the quantity of drink and exercise, have
already been mentioned. It is also liable to be influenced *
by the condition of the nervous system, being sometimes
greatly increased in hysteria, and some other nervous
affections; and at other times diminished. -In some
diseases it is enormously increased; and its increase may
be either attended with an augmented quantity of solid
matter, as in ordinary diabetes, or may be nearly the sole
change, as in the affection termed diabetes insipidus. In
other diseases, ¢.g., the various forms of albuminuria, the
quantity may be considerably diminished. <A febrile con-
dition almost always diminishes the quantity of water;
and a like diminution is caused by any affection which |
draws off a large quantity of fluid from the body through
any other channel than that of the kidneys, ¢.g., the bowels
and the skin.

Fig. 126.* Urea.—Urea is the prin-
cipal solid constituent of the
urine, forming nearly one-
half of the whole quantity of

by which the nitrogen of de-

fluous food is excreted from
the body. For its removal,
the secretion of urine seems
especially provided ; and by its retention in the blood the
most pernicious effects are produced.

Urea, like the other solid constituents of the urine,

* Fig. 126. Crystals of urea.

solid matter. It is also the
most important ingredient, —
since it is the chief substance |

composed tissue and super- |

4 ee

>
LO a

TO aa tee

~

UREA. 3 433

exists in a state of solution. | But it may be procured in
the solid state, and then appears in the form of delicate

ey

silvery acicular crystals, which, under the microscope, |
appear as four-sided prisms (fig. 126). It is obtained in —

this state by evaporating urine carefully to the consistence
of honey, acting on the inspissated mass with four parts
of alcohol, then evaporating the alcoholic solution, and

purifying the residue by repeated solution in water or \

alcohol, and finally allowing it to crystallise. It readily
combines with an acid, like a weak base; and may thus be
conveniently procured in the form of a nitrate, by adding
about half a drachm of pure nitric acid to double that
quantity of urine in a watch glass. The crystals of nitrate
of urea are formed more rapidly if the urine have been
previously concentrated by evaporation.

Urea is colourless when pure; when impure, yellow or
brown: without smell, and of a cooling, nitre-like taste ;
has neither an acid nor an alkaline re-action, and deli-
quesces in a moist and warm atmosphere. At 59° F’. it

requires for its solution less than its weight of water; it is |

dissolved in all proportions by boiling water; but it re-
quires five times its weight of cold alcohol for its solution.
At 248° F. it melts without undergoing decomposition; at
a still higher temperature ebullition takes place, and car-
bonate of ammonia sublimes; the melting mass gradually
acquires a pulpy consistence ; and, if the heat is carefully
regulated, leaves a grey-white powder, cyanie acid.

Urea is identical in composition with cyanate of ammo-
nia, and was first artificially produced by Wohler from this
substance. Thus :—

Cyanate of Ammonia. Urea.
CHNO. H,N = CH,N,0.

The action of heat upon urea in evolving carbonate of
ammonia, and leaving cyanic acid, is thus explained. A
similar decomposition of the urea with development of
carbonate of ammonia ensues spontaneously when urine is

|

/
454 THE URINE. ;

kept for some days after being voided, and explains the
ammoniacal odour then evolved. It is probable, that this
spontaneous decomposition is accelerated by the mucus and
other animal matters in the urine, which, by becoming
putrid, act the part of a ferment and excite a change of
composition in the surrounding compounds. It is chiefly
thus that the urea is sometimes decomposed before it
leaves the bladder, when the mucous membrane is diseased,
and the mucus secreted by it is both more abundant and,
probably, more prone than usual to become putrid. ‘The
same occurs also in some affections of the nervous system,
particularly in paraplegia.

The quantity of urea excreted is, like that of the urine
itself, subject to considerable variation. It is materially
influenced by diet, being greater when animal food is
exclusively used, less when the diet is mixed, and least of
all with a vegetable diet. As a rule, men excrete a larger
quantity than women, and persons in the middle periods of
life a larger quantity than infants or old people (Lecanu).
The quantity of urea does not necessarily increase and
decrease with that of the urine, though on the whole it
would seem that whenever the amount of urine is much
augmented, the quantity of urea also is usually increased

_ (Becquerel); and it appears from observations of Genth,

|

that the quantity of urea, as of urine, may be especially
increased by drinking large quantities of water. In various
diseases, as albuminuria, the quantity is reduced consider-
ably below the healthy standard, while in other affections
it is above it.

The urea appears to be derived from two different sources.
That it is derived in part from the unassimilated elements

_ of nitrogenous. food, circulating with the blood, is shown

in the increase which ensues on substituting an animal or
highly nitrogenous for a vegetable diet; in the much larger
amount, nearly double, excreted by Gaaniivents than Her-
bivora, independent of exercise; and in its diminution to

UREA. 455

about one-half during starvation, or during the exclusion

of non-nitrogenous principles of food. But that it is inj
larger part derived from the disintegration of the azotized |
animal tissues, is shown by the fact that it continues to be.
excreted, though in smaller quantity than usual, when all)
nitrogenous substances are strictly excluded from the food,

as when the diet consists for several days of sugar, starch,
gum, oil, and similar non-azotized vegetable substances
(Lehmann). It is excreted also, even though no food at
all be taken for a considerable time; thus it is found in
the urine of reptiles which have fasted for months; and
in the urine of a madman, who had fasted eighteen days,
Lassaigne found both urea and all the components of
healthy urine. Probably all the nitrogenous tissues fur-
nish a share of urea by their decomposition.

It has been commonly taken for granted that the quan-
tity of urea in the urine is greatly increased by active
exercise; but numerous observers have failed to detect
more than a slight increase under such circumstances ;
and our notions concerning the relation of this excretory
product to the destruction of muscular fibre, consequent
on the oxercise of the latter, have lately undergone con-
siderable modification. There is no doubt, of course, that
like all parts of the body, the muscles have but a limited
term of existence, and are being constantly renewed, at
the same time that a part of the products of their disin-
tegration appears in the urine in the form of urea. But the
waste is not so fast as it has been frequently supposed to
be; and the theory that the amount of work done by
the muscle is expressed by the quantity of urea excreted
in the urine, and that each act of contraction corresponds
to an equivalent waste of muscle-structure, is founded on
error. (See also chapter on Motion.)

Urea exists ready-formed in the blood, and is simply
abstracted therefrom by the kidneys. It may be detected
in small quantity in the blood, and in some other parts of

on

456 THE URINE.

the body, e.g., the humours of the eye (Millon), even while
the functions of the kindeys are unimpaired: but when
from any cause, especially extensive disease or extirpation
of the kidneys, the separation of urine is imperfect, the
urea is found largely in the blood and in most other fluids
of the body.

Uric Acid.—This, which is another nitrogenous animal
substance, with the for-
mula C;N,H,O,, and was
formerly termed lithic acid,
on account of its existence
in many forms of urinary
calculi, is rarely absent
from the urine of man or
animals, though in the
feline tribe it seems to
be sometimes entirely re-
placed by urea (G. Bird).
Its proportionate quantity
varies considerably in different animals. In man, and
Mammalia generally, especially the Herbivora, it is com-
paratively small. In the whole tribe of birds and of
serpents, on the other hand, the quantity is very large,
greatly exceeding that of the urea. In the urine of grani-
vorous birds, indeed, urea is rarely if ever found, its place
being entirely supplied by uric acid. The quantity of uric
acid, like that of urea, in human urine, is increased by the
use of animal food, and decreased by the use of food free
from nitrogen, or by an exclusively vegetable diet. In
most febrile diseases, and in plethora, it is formed in
unnaturally large quantities; and in gout it is deposited
\ in, and in the tissues around, joints, in the form of urate
\ of soda, of which the so-called chalk-stones of this disease
, are principally composed.

Fig. 127.*

* Fig. 127. Various forms of uric acid crystals.

ee Se eT

“ =. —o- oO te

[ills ls Sil cteng,

URIC ACID. 457

The condition in which uric acid exists in solution in the
urine has formed the subject of some discussion, because
of its difficult solubility in water.

According to Liebig the uric acid exists as urate of soda,
produced, he supposes, by the uric acid, as soon as it is
formed, combining with part of the base of the alkaline
phosphate of soda of the blood. Hippuric acid, which
exists in human urine also, he believes, acts upon the
alkaline phosphate in the same way, and increases still
more the quantity of acid phosphate, on the presence of
which it is probable that a part of the natural acidity of
the urine depends. It is scarcely possible to say whether
the union of uric acid with the base soda and probably
ammonia, takes place in the blood, or in the act of secre-
tion in the kidney: the latter is the more probable
opinion ; but the quantity of either uric acid or urates in
the blood is probably too small to allow of this question
being solved.

The source of uric acid is probably in the disintegrated
elements of albuminous tissues. The relation which uric
acid and urea, oear-to each other is, however, still obscure.
The fact that they often exist together in the same urine,
makes it seem probable that they have different origins or
different offices to perform; but the entire replacement of
either by the other, as of urea by uric acid in the urine of
birds, serpents, and many insects, and of uric acid by urea,
in the urine of the feline tribe of Mammalia, shows that
each alone may discharge all the important functions of

the two.

Owing to its existence in combination in healthy urine,
uric acid for examination must generally be precipitated
from its bases by a stronger acid. Frequently, however,
when excreted in excess, it is deposited in a crystalline
form (fig. 127), mixed with large quantities of urate of
ammonia or soda (fig. 130). In such cases it may be
procured for microscopic examination, by gently warming

458 THE URINE.

the portion of urine containing the sediment ; this dissolves
urate of ammonia and soda, while the comparatively in-
soluble crystals of uric acid subside to the bottom.

The most common form in which uric acid is deposited

in urine, is that of a brownish or yellowish powdery sub- |
stance, consisting of granules of urate of ammonia or soda. |

When deposited in crystals, it is most frequently in
rhombic or diamond-shaped laminz, but other forms are
not uncommon (fig. 127). When deposited from urine,
the crystals are generally more or less deeply coloured,
by being combined with the colouring principles of the
urine.

Fig. 128. Hippuric Acid has long
been known to exist in the
urine of herbivorous animals
in combination with soda.
Liebig has shown that it also
exists naturally in the urine
of man, in quantity equal to
the uric acid, and Weismann’s
observations agree with this.
It is a nitrogenous compound
with the formula C,H,NO,.
It is closely allied to benzoic
acid ; and this substance when introduced into the system,
is excreted by the kidneys as hippuric acid (Ure). Its
source is not satisfactorily determined: in part it is pro-
bably derived from some constituents of vegetable diet,
though man has no hippuric acid in his food, nor, com-
monly, any benzoic acid that might be converted into it ;
in part from the natural disintegration of tissues, inde-
pendent of vegetable food, for Weismann constantly found
an appreciable quantity, even when living on an exclusively
animal diet.

Se ee ee ee

* Fig. 128. Crystals of hippuric acid.

COLOURING MATTER: MUCUS: EXTRACTIVE. 459

The nature and composition of the colouring matter of
urine are involved in some obscurity. It is probably closely
related to the colouring matter of the blood.

The mucus in the urine con- Fig. 129.*
sists principally of the epi- - ;
thelial débris of the mucous
surface of the urinary pas-
sages. Particles of epithe-
lium, in greater or less abun-
dance, m aybe dectectedin most
samples of urine, especially if
it has remained at rest for
some time, and the lower
strata are then examined (fig.
129). As urine cools, the
mucus is sometimes seen suspended in it as a delicate opaque
cloud, but generally it falls. In inflammatory affections of
the urinary passages, especially of the bladder, mucus in
large quantities is poured forth, and speedily undergoes
decomposition. The presence of the decomposing mucus
excites (as already stated) chemical changes in the urea,
whereby ammonia, or carbonate of ammonia, is formed,
which, combining with the excess of acid in the super-
phosphates in the urine, produces insoluble neutral or
alkaline phosphates of lime and magnesia, and phosphate
of ammonia and magnesia. These, mixing with the mucus,
constitute the peculiar white, viscid, mortar-like substance
which collects upon the mucous surface of the bladder, and
is often passed with the urine, forming a thick, tenacious
sediment.

Besides mucus and colouring matter, urine contains a
considerable quantity of animal matter, usually described
under the obscure name of animal extractive. The investi-
gations of Liebig, Heintz, and others, have shown that

* Fig. 129. Mucus deposited from urine.

460 THE URINE.

some of this ill-defined substance consists of Creatin and
Creatinin, two erystallizable substances derived, probably,
from the metamorphosis of muscular tissue. These sub-
stances appear to be intermediate between the proper
elements of the muscles, and, perhaps, of other azotized
tissues and urea: the first products of the disintegrating
tissues probably consisting not of urea, but of Creatin and
Creatinin, which subsequently are partly resolved into

urea, partly discharged, without change, in the urine.

The names of some other substances of which there are
commonly traces in the urine, will be found in Table IL.,
p- 451. It has been shown by Scherer that much of the
substance classed as extractive matter of the urine, is the
peculiar colouring matter, probably derived from the
heemo-globin of the blood.

Saline Matter.—The sulphuric acid in the urine is com-
bined chiefly or entirely with soda, and potash: forming
salts which are taken in very small quantity with the food,
and are scarcely found in other fluids or tissues of the
body ; for the sulphates commonly enumerated among the
constituents of the ashes of the tissues and fluids are, for
the most part or entirely, produced by the changes that
take place in the burning. Dr. Parkes, indeed, considers
that only about one-third of the sulphuric acid found in
the urine is derived directly from the food. Hence the
greater part of the sulphuric acid which the sulphates in
the urine contain, must be formed in the blood, or in the
act of secretion of urine; the sulphur of which the acid is
formed, being probably derived from the decomposing
nitrogenous tissues, the other elements of which are re-
solved into urea and uric acid. It may be in part derived
also, as Dr. Parkes observes, from the sulphur-holding
taurin and cystin which can be found in the liver, lungs,
and other parts of the body, but not generally in the
excretions ; aud which, therefore, must be broken up. The
oxygen is supplied through the lungs, and the heat gene-

~

9 iii aaicteiiaiial

\
ALKALINE AND EARTHY PHOSPHATES. 461

tated during combination with the sulphur, is one of the
subordinate means by which the animal temperature is
maintained.

Besides the sulphur in these salts, some also appears to
be in the urine, uncombined with oxygen; for after all the
sulphates have been removed from urine, sulphuric acid
may be formed by drying and burning it with nitre. Mr.
Ronalds believes that from three to five grains of sulphur
are thus daily excreted. The combination in which it
exists. is uncertain: possibly it is in some compound
analogous to cystin or cystic oxide (p. 462).

The phosphorie acid in the urine is combined partly with
the alkalies, partly with the alkaline earths—about four or
five times as much with the former as with the latter. In
blood, saliva, and other alkaline fluids of the body, phos-
phates exist in the form of alkaline, or neutral acid salts.
In the urine they are acid salts, viz., the phosphates of
sodium, ammonium, calcium and magnesium, the excess

of acid being, according to Liebig, due to the appropriation

of the alkali with which the phosphoric acid in the blood
is combined, »y the several new acids which are formed or
discharged at the kidneys, namely, the uric, hippuric, and
sulphuric acids, all of which he supposes to be neutralized
with soda. -

The presence of the acid phosphates accounts, in great
measure, or, according to Liebig, entirely, for the acidity
of the urine. The phosphates are taken largely in both
vegetable and animal food; some thus taken, are excreted
at once; others, after being transformed and incorporated
with the tissues. Phosphate of calcium forms the principal
earthy constituent of bone, and from the decomposition of
the osseous tissue the urine derives a large quantity of this
salt. The decomposition of other tissues also, but espe-
cially of the brain and nerve-substance, furnishes large
supplies of phosphorus to the urine, which phosphorus is
supposed, like the sulphur, to be united with oxygen, and

462 THE URINE. ;

then combined with bases. This quantity is, however,
liable to considerable vari-
ation. Any undue exercise of
the mind, and all circum-
stances producing nervous
exhaustion, increaseit. The
earthy phosphates are more
abundant after meals, whe-
ther on animal or vegetable
food, and are diminished after
long fasting. The alkaline
phosphates are increased after
animal food, diminished after
vegetable food. Exercise increases the alkaline, but. not
the earthy phosphates (Bence Jones). Phosphorus uncom-
bined with oxygen appears, like sulphur, to be excreted in
the urine (Ronalds). When the urine undergoes alkaline
fermentation, phosphates are deposited in the form of an
urinary sediment consisting chiefly of phosphate of ammonia
and magnesia (triple phosphate) (fig. 130). This compound
does not, as such, exist in healthy urine, The ammonia is
chiefly or wholly derived from the decomposition of urea
(p. 453).

' The chlorine of the urine occurs chiefly in combination
with sodium, but slightly also with ammonium, aud,
perhaps, potassium. As the chlorides exist largely in
food, and in most of the animal fluids, their occurrence in
the urine is easily understood.

Cystin (fig. 132) is an occasional constituent of urine. It
resembles taurin in containing a large quantity of sulphur—
more than 25 per cent. It does not exist in healthy urine.

Another common morbid constituent of the urine is

Fig. 130.* —

* Fig. 130. Urinary sediment of triple phosphates (Iarge prismatic
crystals) and urate of ammonia, from urine which had undergone
alkaline fermentation.

We es ke

rn a

THE NERVOUS SYSTEM. 463

oxalic acid, which is frequently deposited in combination

Fig. 131.* Fig. 132.F

with lime (fig. 131) as an urinary sediment. Like cystin,
but much more commonly, it is the chief constituent of
certain calculi.

A small quantity of gas is naturally present in the urine
in a state of solution. It consists chiefly of carbonic acid
and nitrogen.

CHAPTER XVI.
THE NERVOUS SYSTEM.

THE nervous system consists of two portions or systems,
the cerebro-spinal and the sympathetic or ganglionic, each of
which (though they have many things in common) pos-
sesses certain peculiarities in structure, mode of action, and
range of influence.

The cerebro-spinal system includes the brain and spinal
cord, with the nerves proceeding from them, and the several
ganglia seated upon these nerves, or forming part of the

* Fig. 131. Crystals of oxalate of lime.
+ Fig. 132. Crystals of cystin.

4604 THE NERVOUS SYSTEM.

substance of the brain. It was denominated by Bichat
the nervous system of animal life; and includes all the
nervous organs in and through which are performed the
several functions with which the mind is more immediately
connected, namely, those relating to sensation and volition,
and the mental acts connected with sensible things.

The sympathetic or ganglionic portion of the nervous sys-
tem, which Bichat named the nervous system of organic*
life, consists essentially of a chain of ganglia connected
by nervous cords, which extend from the cranium to the
pelvis, along each side of the vertebral column, and from
which, nerves with ganglia proceed to the viscera in the
thoracic, abdominal, and pelvic cavities. By its distribu-
tion, as well as by its peculiar mode of action, this system
is less immediately connected with the mind, either as con-
ducting sensations or the impulses of the will; it is more
closely connected than the cerebro-spinal system is with
the processes of organic life.

The differences, however, between these two systems,
are not essential: their actions differ in degree and object
more than in kind or mode.

Elementary Structures of the Nervous System.

The organs of the nervous system or systems are com-
posed essentially of two kinds of structure, vesicular and
fibrous; both of which appear essential to the construction
of even the simplest nervous system. The vesicular

* The term organic is often used in connection with a function,
such as digestion or secretion, which belongs to all organised beings
_alike ; while the term animal function, or animal life, is used in con-

nection with such qualities as volition or motion, which seem altogether ©

or in great part to belong only to animals. The terms which have been
thus used in this general way, are often loosely applied to special
tissues. Thus organic nerve-fibres are those which are distributed
especially to organs concerned in the discharge of the functions of
organic, as distinguished from animal life; and the term is still more
commonly applied to one kind of muscular fibre.

~~
Bl i ee

STRUCTURE OF NERVE-FIBRES. 465

structure is usually collected in masses, and mingled with
the fibrous structure, as in the brain, spinal cord, and the
several ganglia; and these masses constitute what are
termed nerve-centres, being the organs in which it is sup-
posed that nervous force may be generated, and in which
are accomplished all the various reflections and other
modes of disposing of impressions when they are not simply
conducted along nerve-fibres. The fibrous nerve-substance,
besides entering into the composition of the nervous centres,
forms along the nerves, or cords of communication, which
connect the various nervous centres, and are distributed in
the several parts of the body, for the purpose of conveying
nervous force to them, or of transmitting to the nervous
centres the impressions made by stimuli.

Along the nerve-fibres impressions or conditions of ex-
citement are simply conducted : in thexnervous centres they
may be made to deviate from their direct course, and be
variously diffused, reflected, or otherwise disposed of.

a

Nerves are constructed of minute fibres or tubules full of
nervous matter, arranged in parailel or interlacing bundles,
which bundles are connected by intervening connective
tissue, in which their principal blood-vessels ramify. A
layer of the areolar, or of strong fibrous tissue, also sur-
rounds the whole nerve, and forms a sheath or neurilemma
for it. In most nerves, two kinds of fibres are mingled;
those of one kind being most numerous in, and charac-
teristic of, nerves of the cerebro-spinal system; those of
the other, most numerous in nerves of the sympathetic
system.

The fibres of the first kind appear to consist of tubules
of a pellucid simple membrane, within which is contained
the proper nerve substance, consisting of transparent oil-
like, and apparently homogeneous, material, which gives
to each fibre the appearance of a fine glass tube filled with
a clear transparent fluid (fig. 133, 4). This simplicity of

HEH

466 THE NERVOUS SYSTEM.

composition is, however, only apparent in the fibres of
a perfectly fresh nerve; for, shortly after death, they
undergo changes which make it probable that their con-
tents are composed of two different materials. The internal
or central part, occupying the axis of the tube, becomes
greyish, while the outer, or cortical portion, becomes
opaque and dimly granular or grumous, as if from a kind
of coagulation. At the same time, the fine outline of the
previously transparent cylindrical tube is exchanged for a
dark double contour (fig. 133, B), the outer line being
formed by the sheath of the fibre, the inner by the margin
of curdled or coagulated medullary substance. The gra-
Fig. 133° nular material shortly collects
A BO into little masses, which distend
| | portions of the tubular mem-
brane, while the intermediate
spaces collapse, giving the fibres
a varicose, or beaded appearance
(fig. 133, c and p), instead of the
previous cylindrical form.

The difference produced in the
contents of the nerve-fibres when
exposed to the same conditions,
has, with other facts, led to the
| opinion now generally adopted,
\ | that the central part or avzis-

| Hi | | cylinder of each nerve-fibre differs

from the outer, portion. The
outer portion is usually called the medullary or white

* Fig. 133. Primitive nerve-tubules. aA. A perfectly fresh tubule
with a single dark outline. 38. A tubule or fibre with a double contour
from commencing post-mortem change. c. The changes further ad-
vanced, producing a varicose or beaded appearance. p. A tubule or
fibre, the central part of which, in consequence of still further changes,
has accumulated in separate portions within the sheath (after Wagner).

eatin

—— = or —

ee a ee.

wp Aer bet ee Oe BE it ht

so rg

STRUCTURE OF NERVE-FIBRES. 467

substance of Schwann, being that to which the peculiar
white aspect of cerebro-spinal nerves is principally due.
The whole contents of the nerve-tubules appear to be ex-
tremely soft, for when subjected to pressure they readily
pass from one part of the tubular sheath to another,
and often cause a bulging at the side of the membrane.
They also readily escape, on pressure, from the ex-
tremities of the tubule, in the form of a grumous or
granular material.

That there is an essential difference in chemical com-
position between the central and circumferential parts of
the nerve-fibre, i.¢., between the axis-cylinder and the
medullary sheath, has of late been clearly shown by Messrs.
Lister and Turner. Their observations, founded on Mr.
Lockhart Clarke’s method of investigating nervous sub-
stance by means of chromic acid and carmine, have shown
that the axis-cylinder of the'nerve-fibre is unaffected by
chromic acid, but imbibes carmine with great facility,
while the medullary sheath is rendered opaque and brown
and laminated by chromic acid, but is entirely untinged
by the carmine. From this difference in their chemical
behaviour, the central and circumferential portions of
the nerve-fibres are readily distingushed on microscopic
examination, the former being indicated by a bright red
carmine-coloured-point, the latter by a pale ring surround-
ing it. The laminated character of the medullary sheath

after treatment with chromic acid is believed by Mr.

Lockhart Clarke to be due to corrugations effected by
the acid, and not to its having a fibrous structure, as
maintained by Stilling.

The size of the nerve-fibres varies, and the same fibres
do not preserve the same diameter through their whole
length, being largest in their course within the trunks
and branches of the nerves, in which the majority measure
from 5,15 to >> of an inch in diameter. As they ap-
proach the brain or spinal cord, and generally also in

HH 2

468 ‘THE NERVOUS SYSTEM.

the tissues in which they are distributed, they gradually
become smaller. In the grey or vesicular substance of the
brain or oat cord, sone generally do not measure more
than from =>$5, to tts of an inch. .

The fibres of the second kind (fig. 134), which oiniaivade
the whole of the branches of the olfactory nerves, the prin-
cipal part of the trunk and branches of the sympathetic
nerves, and are mingled in various proportions in the
cerebro-spinal nerves, differ from the preceding, chiefly in
their fineness, being only about 3 or 4 as large in their
course within the trunks and branches of the nerves; in

Fig. 134.*

the absence of the double contour ; in their contents being
apparently uniform; and in their having, when in bundles,
a yellowish-gréy hue instead of the whiteness of the
cerebro-spinal nerves. These peculiarities make it pro-
bable that they differ from the other nerve-fibres in not
possessing the outer layer of white or medullary nerve-
substance ; and that their contents are composed exclusively

* Fig. 134. Grey, pale, or gelatinous nerve-fibres (from Max -

Schultze), magnified between 400 and 500 diameters. A, from a

branch of the olfactory nerve of the sheep; a, a, two dark-bordered —

or white fibres from the fifth pair, associated with the pale olfactory
fibres. B, from the sympathetic nerve.

1
—

ee

ee — a ee

see,

ee tt el
_ > ,

COURSE OF NERVE-FIBRES. 469

of the substance corresponding with the central portion, or
axis-cylinder of the larger fibres. Yet since many nerve-
fibres may be found which appear intermediate in character
between these two kinds, and since the large fibres, as
they approach both their central and their peripheral end,
gradually diminish in size, and assume many of the other
characters of the fine fibres of the sympathetic system, it
is not necessary to suppose that there must be a material
difference in the office or mode of action of the two kinds
of fibres.

Every nerve-fibre in its course proceeds uninterruptedly
from its origin at a nervous centre to near its destination,

Fig. 135*.

whether this be the periphery of the body, another nervous

centre, or the same centre whence it issued.

* Fig. 135. Small branch of a muscular nerve of the frog, near its
termination, showing divisions of the fibres. «@, into two;.J, into
three ; magnified 350 diameters (from Kolliker).

470 THE NERVOUS SYSTEM.

Bundles, or fasciculi of fibres, run together in the nerves,
but merely lie in apposition with each other; they do not
unite: even when the fasciculi anastomose, there is no
union of fibres, but only an interchange of fibres between
the anastomosing fasciculi. Although each nerve-fibre is
thus single and undivided through nearly its whole course,
yet as it approaches the region in which it terminates,
individual fibres break up into several subdivisions (fig.
135) before their final ending in the different fashions
to be immediately described. The white or medullated
nerve-fibres (fig. 133), moreover, lose their medullary sheath
or white substance of Schwann before their final distribu-
tion, and acquire the characters more or less of the pale or
grey fibres (fig. 134).

At certain parts of their course, nerves form pleauses, in
which they anastomose with each other, and interchange
fasciculi, as in the case of the brachial and lumbar plexuses,
The object of such interchange of fibres is, probably, to
give to each nerve passing off from the plexus, a wider
connection with the spinal cord than it would have if it
proceeded to its destination without such communication
with other nerves. ‘Thus, each nerve by the wideness of
its connections, is less dependent on the integrity of any
single portion, whether of nerve-centre or of nerve-trunk,
from which it may spring. By this means, also, each part
supplied from a plexus has wider relations with the
nerve-centres, and more extensive sympathies; and, by
means of the same arrangement, as Dr. Gull suggests,
groups of muscles may be associated for combined actions ;
every member of the group receiving motor filaments from
the same parts of the nerve-centre,

The terminations of nerve-fibres are their modes
of distribution and connection in the nerve-centres,
and in the parts which they supply: the former are
called their central, the latter their peripheral termina-
tions.

‘ ‘ing A A ipa Sei al ae os 2, tlie

PACINIAN BODIES. A7I

The peripheral termination of nerve-fibres has been

always the subject of considerable discussion and doubt.

The following appear to be the chief modes of ending of
nerve-fibres in the parts they supply :—

1. In fine networks or plexuses; examples of this are
found in the distribution of nerves in muscles, and in
mucous and serous membranes. 2. In special terminal
organs; called touch-corpuscles (fig. 113), end-bulbs (fig. 114),
and Pacinian bodies (figs. 136,137). 3. Incells; asin the eye
and internal ear, and some other parts. 4. In free ends;
as from the fine plexuses in muscles, according to Kélliker.
5. In muscles, a peculiar termination of neryes in small
bodies called motorial end-plates, has been described by
Rouget and others. These small bodies, varying from
soo~p 10-345 Of an inch in diameter, and placed by different
observers outside and inside the sarcolemma, are fixed to
the muscular fibres, one for each, and to them the ex-
tremity of a minute branch of nerve-fibre is attached.
These little plates appear to be formed of an expansion of
the end of a nerve-fibre with a small quantity of con-
nective tissue,

The Pacinian bodies or corpuscles (figs. 136 and 137), to
which reference has been just made, are little elongated oval
bodies, situated on some of the cerebro-spinal and sympa-
thetic nerves, especially the cutaneous nerves of the hands
and feet; and on branches of the large sympathetic plexus
about the abdominal aorta (Kolliker). They often occur
also on the nerves of the mesentery, and are especially
well seen in the mesentery of the cat. They are named
Pacinian, after their discoverer Pacini. Each corpuscle is
attached by a narrow pedicle to the nerve on which it is
situated; it is formed of several concentric layers of fine
membrane, with intervening spaces containing fluid;
through its pedicle passes a single nerve-fibre; which,
after traversing the several concentric layers and their
immediate spaces, enters a central cavity, and, gradually

472° THE NERVOUS SYSTEM.

losing its dark border, and becoming smaller, terminates
at or near the distal end of the cavity, in a knob-like
enlargement, or in a bifurcation. The enlargement com-
monly found at the end of the fibre, is said by Pacini to
resemble a ganglion-corpuscle; but this observation has

Fig. 136.* Fig. 137.+

not been confirmed. The physiological import of these
bodies seems to be still quite obscure.

The central termination of nerve-fibres can be better
considered, after the account of the vesicular nerve
substance,

* Fig. 136. Extremities of a nerve of the finger with Pacinian cor-
puscles attached, about the natural size (adapted from Henle ot
Kolliker).

+ Fig. 137. A magnified view of a single Pacinian corpuscle, showing
its laminated structure, and the termination of the nerve-fibre in its
central cavity (after Bendz).

ee ee ee eee

Sn

a a

ja

STRUCTURE OF NERVE-CENTRES, 473

The vesicular nervous substance contains, as its name
implies, vesicles or corpuscles, in addition to fibres; and a
structure, thus composed of corpuscles and inter-communi-
cating fibres, usually constitutes a nerve-centre: the chief
nerve-centres being the grey matter of the brain and
spinal cord, and the various so-called ganglia. In the|
brain and spinal cord a fine stroma of retiform ‘tissue
called the newroglia extends throughout both the fibrous

Fig. 138.* Fig. 139.¥

and vesicular nervous substance,
and forms a supporting and
investing frame-work for the
whole.

The nerve-corpuscles, which |
give to the ganglia and to |
certain parts of the brain
and spinal cord the peculiar
greyish or reddish-grey aspect by which these parts are |
characterized, are large, nucleated cells, filled with a finely —
granular material, some of which is often dark like pig- ©

* Fig. 138. Nerve-corpuscles form a ganglion (after Valentin), _ In
one a second nucleus is visible. In several the nucleus contains one
or two nucleoli,

+ Fig. 139. Stellate or caudate nerve-corpuscles, with tubular pro-
cesses issuing from them. Besides being filled with granular material
continuous with the contents of the processes, the corpuscles contain
black pigment-matter (after Hannover).

474 THE NERVOUS SYSTEM.

ment: the nucleus, which is vesicular, contains a nucleolus
(fig. 138). Besides varying: much in shape, partly in
consequence of mutual pressure, they present such other
varieties as make it probable either that there are two
different kinds, or that, in the stages of their development,
they pass through very different forms. Some of them are
small, generally spherical or ovoid, and have a regular

uninterrupted outline (fig. 138). These simple nerve-cor- —

puscles are most numerous in the sympathetic ganglia;
Others, which are called caudate or stellate nerve-corpvscles
(fig. 139), are larger, and have one, two, or more long
processes issuing from them, the cells being called respec-
tively unipolar, bipolar, or multipolar ; which processes often
divide and subdivide, and appear tubular, and filled with
the same kind of granular material that is contained within
the corpuscle. Of these processes some appear to taper to
a point and terminate at a greater or less distance from
the corpuscle; some appear to anastomose with similar
offsets from other corpuscles ; while others are believed to
become continuous with nerve-fibres, the prolongation from
the cell by degrees assuming the characters of the nerve-
fibre with which it is continuous.

Functions of Nerve-Fibres.

The office of the nerves as simple conveyors or con-
ductors of nervous impressions is of a two-fold kind.
First, they serve to convey to the nervous centres the
impressions made upon their peripheral extremities, or
parts of their course. Secondly, they serve to transmit
impressions from the brain and other nervous centres to
the parts to which the nerves are distributed.

For this two-fold office of the nerves, two distinct sets of
nerve-fibres are provided, in both the cerebral-spinal and
sympathetic systems. Those which convey impressions

——— oe

.
—————— ES Eee eee hee

——- | |

; FUNCTIONS OF NERVE-FIBRES. 47s

from the periphery to the centre are classed together as
centripetal or afferent nerves. ‘Those fibres, on the other
hand, which are employed to transmit central impulses
to the periphery are classed as centrifugal or efferent
nerves.
Centripetal or afferent nerve-fibres may (a) convey to
the nerve-centres with which they are connected impres-

sions which will give rise to sensation (sensitive nerves), or

(b) they may convey an impression which travels out again
from the nerve-centre by an efferent nerve-fibre, and pro-
duces some effect where the latter is distributed, (see
Section on Reflex Action), or (c) they may convey an im-
pression which will produce a restraining or wmhibitory -
action in the nerve-centre, (inhibitory nerves, p. 131).
Centrifugal or efferent nerves may be (a) for the con-
veyance of impulses to the voluntary and involuntary

“muscles, (motor nerves,) or (b) they may influence nutrition

(trophic nerves), (p. 388,) or (c) they may influence secre-
tion (sometimes called secretory nerves) (p. 400).

With this difference in the functions of nerves, there is
no apparent ditference in the structure of the nerve-fibres
by which it might be explained. Among the cerebro-
spinal nerves, the fibres of the optic and auditory nerves
are finer that those of the nerves of common sénsation ;
but, with these exceptions, no centripetal fibres can be dis-
tinguished in their microscopic or general characters from

‘those of centrifugal nerves.

Nerve-fibres possess no power of generating force in
themselves, or of originating impulses to action: for the
manifestation of their peculiar endowments they require
to be stimulated. They possess a certain property of con-
ducting impressions, a property which has been named
excitability ; but this is never manifested till some stimulus
is applied. Thus, under ordinary circumstances, nerves of
sensation are stimulated by external objects acting upon
their extremities; and nerves of motion. by the will, or

476 THE NERVOUS SYSTEM.

by some force generated in the nervous centres. But
almost all things that can disturb the nerves from their
passive state act as stimuli, and agents the most dissimilar
produce the same kind, though not the same degree of
effect, because that on which they act possesses but one
kind of excitable force. Thus all stimuli—chemical,
mechanical, and electric,—when applied to parts endowed
with sensation, or to sensitive nerves (the connection of the
latter with the brain and spinal cord being uninjured) pro-
duce sensations; and when applied to the nerves of muscles
excite contractions. Muscular contraction is produced by
such stimuli as well when the motor nerve is still in con-
nection with the brain, as when its communication with the
nervous centres is cut off by dividing it: nerves, therefore,
have, by virtue of their excitability, the property of exciting
contractions in muscles to which they are distributed; and
the part of the divided motor nerve which is connected
with the muscle will still retain this power, however much
we may curtail it.

Mechanical irritation, when so violent as to injure the
texture of the primitive nerve-fibres, deprives the centri-
petal nerves of their power of producing sensations when
irritation is again applied at a point more distant from the
brain than the injured spot; and in the same way, no
irritation of a motor nerve will excite contraction of the
muscle to which it is distributed, if the nerve has been
compressed and bruised between the point of irritation and
the muscle ; the effect of such.an injury being the same as
that of division.

The action of nerves is also excited by temperature. Thus,
when heat is applied to the nerve going to a muscle, or to
the muscle itself, contractions are produced. These con-
tractions are very violent when the flame of a candle is
applied to the nerve, while less elevated degrees of heat,
—for example, that of a piece of iron merely warmed,—
do not irritate sufficiently to excite action of the muscles.

FUNCTIONS OF NERVE-FIBRES. 477

The application of cold has the same effect as that of heat.
The effect of the local action of excessive or long-continued
cold or heat on the nerves is the same as that of destructive
mechanical irritation. The sensitive and motor power in
the part is destroyed, but the other parts of the nerve retain
their excitability; and, after the extremity of a divided
nerve going to a muscle has been burnt, contractions of
the muscle may be excited by irritating the nerve below
_ the burnt part.

Chemical Stimuli excite the action of both afferent and
efferent nerves as mechanical irritants do; provided their
effect is not so strong as to destroy the structure of the
nerve to which they are applied. A like manifestation of
nervous power is produced by electricity and by magnetism.

Some of these laws regulating the excitability of nerves,
and their power of manifesting their functions, require
further notice, with several others which have not yet been
alluded to. Certain of the laws and conditions of actions
relate to nerves both centrifugal and centripetal, being de-
pendent on properties common to all nerve-fibres ; while
of others, some are peculiar to nerves of motion, some to
nerves of sensation.

It is a law of action in all nerve-fibres, and corresponds
with the continuity and simplicity of their course, that an
impression made on any fibre, is simply and uninterruptedly
transmitted along it, without being imparted or diffused to
any of the fibres lying near it. In other words, all nerve-
fibres are mere conductors of impressions. Their adaptation
to this purpose, is, perbaps, due to the contents of each
fibre being completely isolated from those of adjacent
fibres by the membrane or sheath in which each is enclosed,
and which acts, it may be supposed, just as silk, or other
non-conductors of electricity do, which, when covering a
wire, prevent the electric condition of the wire from being
conducted into the surrounding medium.

478 THE NERVOUS SYSTEM.

Nervous force travels along nerve-fibres with considerable
velocity. Helmholtz and Baxt have estimated the average
rate of conduction of electrical impressions in human motor
nerves at 111 feet per second: this result agreeing very
closely with that previously obtained by Hirsch. Dr.
Rutherford’s observations agree with those of Von Wittich,
that the rate of transmission in sensory nerves is about 140
feet per second.

Nerve-fibres convey only one kind of impression. Thus,
a motor fibre conveys only motor impulses, that is, such as
may produce movements in contractile parts: a sensitive
fibre transmits none but such as may produce sensation, if
they are propagated to the brain. Moreover, the fibres of
a nerve of special sense, as the optic or auditory, convey
only such impressions as may produce a peculiar sensation,
e.g., that of light or sound. While the rays of light and
the sonorous vibrations of the air are without influence on
the nerves of common sensation, the other stimuli, which
may produce pain when applied to them, produce, when
applied to these nerves of special sense, only morbid sensa-
tions of light, or sound, or taste, according to the nerve
impressed.

Of the laws of action peculiar to nerves of sensation and
ef motion respectively, many can be ascertained only by
experiments on the roots of the nerves. For it is only at
their origin that the nerves of sensation and of motion are
distinct ; their filaments, shortly after their departure from
the nervous centres, are mingled together, so that nearly
all nerves, except those of the special senses, consist of
both sensitive and motor filaments, and are hence termed
mixed nerves.

Nerves of sensation appear able to convey impressions °

only from the parts in which they are distributed, towards
the nerve-centre from which they arise, or to which they
tend. Thus, when a sensitive nerve is divided, and irrita-

FUNCTIONS OF NERVE-FIBRES. AIG
tion is applied to the end of the proximal portion, i.e., of
the portion still connected with the nervous centre, sensa-
tion is perceived, or a reflex action ensues; but, when the
end of the distal portion of i divided nerve is irritated,

no effect appears.

When an impression is made upon any part of the course
of a sensitive nerve, the mind may perceive it as if it were
made not only upon the point to which the stimulus is ap-
plied, but also upon all the points in which the fibres of the
irritated nerve are distributed: in other words, the effect -
is the same as if the irritation were applied to the parts
supplied by the branches of the nerve. When the whole
trunk of the nerve is irritated, the sensation is felt at all
the parts which receive branches from it; but when only
individual portions of the trunk are irritated, the sensation
is perceived at those parts only which are supplied by the
several portions. Thus, if we compress the ulnar nerve
where it lies at the inner side of the elbow-joint, behind
the internal condyle, we have the sensation of ‘pins and
needles,” or of a shock, in the parts to which its fibres are _
distributed, naiaely, in the palm and back of the hand,
and in the fifth and ulnar half of the fourth finger. When
stronger pressure is made, the sensations are felt in the
fore-arm also; and if the mode and direction of the pres-
sure be varied, the sensation is felt by turns in the fourth
finger, in the fifth, and in the palm of the hand, or in the
back of the hand, according as different fibres or fasciculi
of fibres are more pressed upon than others.

It is in accordance with this law, that when parts are
deprived of sensibility by compression or division of the
nerve supplying them, irritation of the portion of the nerve
connected with the brain still excites sensations which are
felt as if derived from the parts to which the peripheral
extremities of the nerve-fibres are distributed. Thus,
there are cases of paralysis in which the limbs are totally
insensible to external stimuli, yet are the seat of most

480 THE NERVOUS SYSTEM.

violent pain, resulting apparently from irritation of the |
sound part of the trunk of the nerve still in connection
with the brain, or from irritation of those parts of the
nervous centre from which the sensitive nerve or nerves
which supply the paralysed limbs originate.

An illustration of the same law is also afforded by the
cases in which division of a nerve for.the cure of neuralgic
pain is found useless, and in which the pain continues or
returns, though portions of the nerve be removed. In
such cases, the disease is probably seated nearer the nervous

- centre than the part at which the division of the nerve is
made, or it may be in the nervous centre itself. When the
cause of the neuralgia is seated in the trunk of the nerve—
for example, of the facial or infra-orbital nerve—division
of the branches can be of no service; for the stump remain-
ing in connection with the brain, and containing all the
fibres distributed in the branches of the nerve to the skin,
continues to give rise, when irritated, to the same sensa-
tions as are felt when the peripheral parts themselves are
affected. Division of a nerve prevents the possibility of
external impressions on the cutaneous extremities of its
fibre being felt; for these impressions can no longer be

communicated to the brain: but the same sensations which
were before produced by external impressions may arise
~_ from internal causes. In the same way may be explained
the fact, that when part of a limb has been removed by
amputation, the remaining portions of the nerves which
ramified in it may give rise to sensations which the mind
refers to the lost part. When the stump and the divided
nerves are inflamed, or pressed, the patient complains of
pain felt as if in the part which has been removed. When
the stump is healed, the sensations which we are accus-
tomed to have in a sound limb are still felt; and tingling
and pains are referred to the parts that are lost, or to par-
ticular portions of them, as to single toes, to the sole of
the foot, to the dorsum of the foot, etc.

EE

ee

’
a

FUNCTIONS OF NERVE-FIBRES. A8I

But (as Volkmann shows) it must not be assumed, as it
often has been, from these examples, that the mind has no
power of discriminating the very point in the length of any
nerve-fibre to which an irritation is applied. Even in the
instances referred to, the mind perceives the pressure of a
nerve at the point of pressure, as well as in the seeming
sensations derived from the extremities of the fibres: and
in stumps, pain is felt in the stump, as well as, seemingly,
in the parts removed. It is not quite certain whether those
sensations are perceived by the nerve-fibres which are on
their way to be distributed elsewhere, or by the sentient
extremities of nerves which are themselves distributed to
the many trunks of the nerves, the nervi nervorum. The
latter is the more probable supposition.

The habit of the mind to refer impressions received
through the sensitive nerves to the parts from which im-
pressions through those nerves are, or were, commonly
received, is further exemplified when the relative position
of the peripheral extremities of sensitive nerves is changed
artificially, as in the transposition of portions of skin. When
in the restoration of a nose, a flap of skin is turned down
from the forehead and made to unite with the stump of the
nose, the new nose thus formed has, as long as the isthmus
of skin by which it maintains its original connections re-
mains undivided, the same sensations as if it were still on
the forehead; in other words, when the nose is touched,
the patient feels the impression as if it were made on the
forehead. When the communication of the nervous fibres
of the new nose with those of the forehead is cut off by
division of the isthmus of skin, the sensations are no longer
referred to the forehead; the sensibility of the nose is at
first absent, but is gradually developed.

When, in a part of the body which receives two sensitive
nerves, one is paralysed, the other may or may not be in-
adequate to maintaim the sensibility of the entire part; the

extent to which the sensibility is preserved corresponding
yt

i

482 THE NERVOUS SYSTEM.

probably with the number of the fibres unaffected by the
paralysis. Thus when the ulnar nerve, which supplies the
fifth and a part of the fourth finger, is divided, the sensibility
of those parts is not preserved through the medium of the
branches which the ulnar derives from the median nerve;
but the' fourth and fifth fingers are permanently deprived

f of sensibility. On the other hand, there are instances in

ca

which the trunk of the chief sensitive nerve supplied to a
part having been divided, the sensibility of the part is
still preserved by intercommunicating fibres from a neigh-
bouring nerve-trunk. Thus, a case is related by Mr.
Savory in which, after excision of a portion of the mus-
culo-spiral nerve, the sensibility of some of the parts
supplied by it, although impaired, was not altogether lost,
probably on account of those fibres from the external
cutaneous nerve which are mingled with the radial branch
of the musculo-spiral. One of the uses of a nervous
plexus (p. 470) is here well illustrated.

Several of the laws of action in motor nerves correspond
with the foregoing. Thus, the motor influence is propa-
gated only in the direction of the fibres going to the
muscles ; by irritation of a motor nerve, contractions are
excited in all the muscles supplied by the branches given
off by the nerve below the point irritated, and in those
muscles alone: the muscles supplied by the branches
which come off from the nerve at a higher point than
that irritated, are never directly excited to contraction.
No contraction, for instance, is produced in the frontal
muscle by irritating the branches of the facial nerve that
ramify upon the face; because that muscle derives its
motor nerves from the trunk of the facial previous to these
branches. So, again, because the isolation of motor nerve-
fibres is as complete as that of sensitive ones, the irritation

of a part of the fibres of the motor nerve does not affect

the motor power of the whole trunk, but only that of the
portion to which the stimulus is applied. And it is from

——— ee

FUNCTIONS OF NERVE-CENTRES. 483

the same fact that, when a motor nerve enters a plexus
and contributes with other nerves to the formation of a
nervous trunk proceeding from the plexus, it does not
impart motor power to the whole of that trunk, but only
retains it isolated in the fibres which form its continuation
in the branches of that trunk.

Functions of Nerve-centres.

As already observed (p. 473), the term nerve-centre is
applied to all those parts of the nervous system which
‘contain ganglion-corpuscles, or vesicular nerve-substance,
4.é., the brain, spinal cord, and the several ganglia which
belong to the cerebro-spinal and the sympathetic systems.
Each of these nervous centres has a proper range of
‘functions, the extent of which bears a direct proportion to
‘the number of nerve-fibres that connect it with the various
‘organs of the body, and with other nervous centres; but
‘they all have certain general properties and modes of action
common to them as nervous centres.

It is generally regarded as the property of nervous
centres that they originate the impulses by which muscles
may be excited to action, and by which the several functions
of organic life may be maintained. Hence, they are often
called sowrces or originators of nervous power or force. But
the instances in which these expressions can be used are
very few, and, strictly speaking, do not exist at all. The
brain does not issue any force, except when itself im-
pressed by some force from within, or stimulated by an
impression from without; neither without such previous
impressions do the other nerve-centres produce or issue
motor impulses. The intestinal ganglia, for example, do
not give out the nervous force necessary to the contractions
of the intestines, except when they receive, through their

centripetal nerves, the stimuli of substances in the intestinal
112

eee
OT =
—"

~
\

484 THE NERVOUS SYSTEM.

canal. So, also, the spinal cord ; for a decapitated animal
lies motionless so long as no irritation is applied to its
centripetal nerves, though the moment they are touched
movements ensue.

The more certain and general office of all the nervous
centres is that of variously disposing and transferring the
impressions that reach them through the several centri-
petal nerve-fibres. In nerve-fibres, as already said, im-
pressions are only conducted in the simple isolated course
of the fibre; in all the nervous centres an impression may ~
be not only conducted, but also communicated: in the
brain alone it may be perceived.

Conduction in or through nerve-centres may be thus simply
illustrated. The food in a given portion of the intestines,
acting as a stimulus, produces a certain impression on the
nerves in the mucous membrane, which impression is
conveyed through them to the adjacent ganglia of the
sympathetic. In ordinary cases, the consequence of such
an impression of the ganglia is the movement of the
muscular coat of that and the adjacent part of the canal.
But if irritant substances be mingled with the food, the
sharper stimulus produces a stronger impression, and this
is conducted through the nearest ganglia to others more
and more distant; and, from all these, motor impulses |
issuing, excite a wide-extended and more forcible action
of the intestines. Or even through all the sympathetic
ganglia, the impression may be further conducted to the
ganglia of the spinal nerves, and through them to the
spinal cord, whence may issue motor impulses to the
abdominal and other muscles, producing cramp. And yet
further, the same morbid impression may be conducted
through the spinal cord to the brain, where the mind may
perceive it. In the opposite direction, mental influence
may be e conducted ted from the brain through.a a.

more Jaa of the sympathetic—to produce the influence

ee ia

TRANSFERENCE OF IMPRESSIONS. 485

of the mind on the digestive and other organic functions.
In short, in all cases in which the mind either has
cognizance of, or exercises influence on, the processes
carried on in any part supplied with sympathetic nerves,
there must be a conduction of impressions through all the
nervous centres beween the brain and that part. It is
probable that in this conduction through nervous centres
the impression is not propagated through uninterrupted
nerve-fibres, but is conveyed through successive nerve-
vesicles and connecting nerve-filaments; and in some
instances, and when the stimulus is exceedingly powerful,
the conduction may be effected as quickly as through con-
tinuous nerve-fibres..

But instead of, or as well as, being conducted, impres-
sions made on nervous centres may be communicated from
the fibres that brought them, to others; and in this com-
munication may be either transferred, diffused, or reflected.

The transference of impressions may be illustrated by the

_pain in the knee, which is a common sign of disease of the

hip. In this case the impression made by the disease on the
nerves of the,nip-joint is conveyed to the spinal cord;

‘there it is transferred to the central ends or connections of

the nerve-fibres distributed about the knee. Through these
the transferred impression is conducted to the brain, and
the mind, referring the sensation to the part from which it
usually through these fibres receives impressions, feels as
if the disease and the source of pain were inthe knee. At
the same time that it is transferred, the primary impression
may be also conducted; and in this case the pain is felt
in both the hip and the knee. So, not unfrequently, if
one touches a small pimple, that may be seated in the
trunk, a pain will be felt in as small a spot on the arm, or
some other part of the trunk. And so, in whatever part of
the respiratory organs an irritation may be seated, the
impression it produces is transferred to the nerves of the
larynx ; and then the mind perceives the peculiar sensation

ei —

486 THE NERVOUS SYSTEM.

of tickling in the glottis, which best, or almost alone, ex-
cites the act of coughing. Or, again, when the sun’s light
falls strongly on the eye, a tickling may be felt in the nose,
exciting sneezing. In all these cases, the primary impres-
sion may be conducted as well as transferred; and in all it
is transferred to a certain set of nerves which generally ap-

. pear to be in some purposive relation with the nerves first

impressed. |
The diffusion or radiation of impressions is shown when
an impression received at a nervous ceutre is diffused to
many other fibres in the same centre, and produces sensa-
tions extending far beyond, or in an indefinite area around,
the part from which the primary impression was derived.
Hence, as in the former cases, result various kinds of what
have been denominated sympathetic sensations. Some-
times such sensations are referred to almost every part of
the body: as in the shock and tingling of the skin pro-
duced by some startling noise. Sometimes only the parts
immediately surrounding the point first irritated partici-
pate in the effects of the irritation; thus, the aching of a
tooth may be accompanied by pain in the adjoining teeth,
and in all the surrounding parts of the face; the explana-
tion of such a case being, that the irritation conveyed to the
brain by the nerve-fibres of the diseased tooth is radiated
to the central ends of adjoining fibres, and that the mind
perceives this secondary impression as if it were derived
from the peripheral ends of the fibres. Thus, also the
pain of a calculus in the ureter is diffused far and wide.

All the preceding examples represent impressions com-
municated from one sensitive fibre to others of the same
kind; or from fibres of special sense to those of common
sensation. A similar communication of impressions from
sensitive to motor fibres, constitutes reflection of impressions,
displays the important functions common to all nervous.

centres as reflectors, and produces reflex movements. In the

>

————— re a, ae

so

sume.
a ra

—

i a dada di: ee ee ee

REFLECTION OF IMPRESSION. 487

axtent and direction of such communications, also, pheno-
mena corresponding to those of transference and diffusion
to sensitive nerves, are observed in the phenomena of
reflection. For, as in transference, the reflection may take
place from a certain limited set of sensitive nerves to a
corresponding and related set of motor nerves; as when in
consequence of the impression of light on the retina, the
iris contracts, but no other muscle moves. Or, as in diffu-
sion or radiation, the reflection may bring widely-extended
muscles into action: as when an irritation in the larynx
brings all the muscles engaged in expiration into coincident
movement.

It will be necessary, hereafter, to consider in detail so
many of the instances of the reflecting power of the several
nervous centres, that it may be sufficient here to mention
only the most general rules of reflex action :—

1. For the manifestation of every reflex muscular action,
three things are necessary ; (1), one or more perfect centri-
petal nerve-fibres, to convey an impression; (2), a nervous
centre to which this impression may be conveyed, and by
which it may be reflected; (3), one or more centrifugal
nerve-fibres, upon which this impression may be reflected,
and by which it may be conducted to the contracting tissue.
In the absence of any one of these three conditions, a proper
reflex movement could not take place; and whenever im-
pressions made by external stimuli on sensitive nerves give

rise to motions, these are never the result of the direct |
reaction of the sensitive and motor fibres of the nerves on |

each other ; in all such cases the impression is conveyed by
the sensitive fibres to a nervous centre, and is therein com-
municated to the motor fibres.

2. All reflex actions are essentially involuntary, and may
be accomplished independently of the will, though most of
them admit of being modified, controlled, or prevented by
a voluntary effort.

_ 8. Reflex actions performed in health have, for the most

488 THE NERVOUS SYSTEM.

part,-a distinct purpose, and are adapted to secure some
end desirable for the well-being of the body; but, in
disease, many of them are irregular and purposeless. As
an illustration of the first point, may be mentioned move-
ments of the digestive canal, the respiratory movements,
and the contraction of the eyelids and the pupil to exclude
many rays of light, when the retina is exposed to a bright
glare. These and all other normal reflex acts afford also
examples of the mode in which the nervous centres combine
and arrange co-ordinately the actions of the nerve-fibres,
so that many muscles may act together for the common end.
Another instance of the same kind is furnished by the
spasmodic contractions of the glottis on the contact of
carbonic acid, or any foreign substance, with the interna]
substance of the epiglottis or larnyx. Examples of the
purposeless irregular nature of morbid reflex action are
‘seen in the convulsive movements of epilepsy, and in the
spasms of tetanus and hydrophobia.

4. Reflex muscular acts are often more sustained than
those produced by the direct stimulus of muscular nerves.
As Volkmann relates, the irritation of a muscular organ,
or its motor nerve, produces contraction lasting only so
long as the irritation continues; but irritation applied to
a nervous centre through one of its centripetal nerves, may
excite reflex and harmonious contractions, which last some
time after the withdrawal of the stimulus.

CEREBRO-SPINAL NERVOUS SYSTEM.

The physiology of the cerebro-spinal nervous system
includes that of the spinal cord, medulla oblongata, and
brain, of the several nerves given off from each, and of the

* Fig. 140. View of the cerebro-spinal axis of the nervous system
(after Bourgery).—The right half of the cranium and trunk of the
body has been removed by a vertical section ; the membranes of the
brain and spinal marrow have also been removed, and the roots and first
part of the fifth and ninth cranial, and of all the spinal nerves of the
right side, have been dissected out and laid separately on the wall of the

THE CEREBRO-SPINAL AXIS. 489

Fig. 140.*

Pons Vurolé - Nek
Me dull. Oblong
Certhellum-->

=f
| Upper Extremity
of Spiral Cord

\\. | Ast Dorsal
SS Vertebra

\

'

~ === 4st Lumbar
=A Vertehro

Lower Extremity - -
| of Shinal Cord

-- Sacrum

skull and on the several vertebre opposite to the place of their natural

exit from the cranio-spinal cavity.

* 490 THE NERVOUS SYSTEM.

ganglia on those nerves. It will be convenient to speak
first of the spinal cord and its nerves.

~ Spinal Cord and its Nerves.

The spinal cord is a cylindriform column of nerve-sub-
stance, connected above with the brain through the medium
of the medulla oblongata, terminating below, about the
lower border of the first lumbar vertebra, in a slender
filament of grey or vesicular substance, the filum terminale
which lies in the midst of the roots of many nerves form-
ing the cauda equina. The cord is composed of fibrous
and vesicular nervous substance, of which the former is
situated externally, and constitutes its chief portion, while
the latter occupies its central or axial portion, and is so
arranged, that on the surface of a transverse section of
the cord it appears like two somewhat crescentic masses
connected together by a narrower portion or isthmus (fig.
I4I).

Passing through the centre of this isthmus in a longitu-
dinal direction is a minute canal, which is continued through
the whole length of the cord, and opens above into the
space at the back of the medulla oblongata and pons
Varolii, called the fourth ventricle. It is lined by a layer
of cylindrical ciliated epithelium.

The spinal cord consists of two exactly symmetrical
halves united in the middle line by a commissure, but
separated anteriorly and posteriorly by a vertical fissure ;
the posterior fissure being deeper, but less wide and dis-
tinct than the anterior. Each half of the spinal cord is
marked on the sides (obscurely at the lower part, but dis-
tinctly above) by two longitudinal furrows, which divide
it into three portions, columns, or tracts, an anterior, middle
or lateral, and posterior. From the groove between the
anterior and lateral columns spring the anterior roots of
the spinal nerves; and just in front of the groove between

‘

STRUCTURE OF THE SPINAL CORD. 491

the lateral and posterior column arise the posterior roots
of the same: a pair of roots on each side corresponding to
each vertebra (fig. 141).

The fibrous part of the cord contains continuations of the
innumerable fibres of the spinal nerves issuing from it, or
entering it; but it is, probably, not formed of them exclu-

Fig. 141.*

* Vig. 141. Different views of a portion of the spinal cord from the
cervical region, with the roots of the nerves slightly enlarged (from
Quain). In A, the anterior surface of the specimen is shown ; the an-
terior nerve-root of its right side being divided ; in B, a view of the
right side is given ; in c, the upper surface is shown ; in p, the nerve-
roots and ganglion are shown from below. 1. the anterior median
fissure ; 2, posterior median fissure ; 3, anterior lateral depression, over

» which the anterior nerve-roots are seen to spread ; 4, posterior lateral

groove, into which the posterior roots are seen to sink; 5, anterior
roots passing the ganglion; 5’, in A, the anterior root divided ; 6, the
posterior roots, the fibres of which pass into the ganglion 6’; 7, the
united or compound nerve; 7’, the posterior primary branch, seen in
A and D to be derived in part from the anterior and in part from the
posterior root.

492 THE NERVOUS SYSTEM.

sively; nor is it a mere trunk, like a great nerve, through
which they may pass to the brain. It is, indeed, among
the most difficult things in structural anatomy to determine
the course of individual nerve-fibres, or even of fasciculi
of fibres, through even a short distance of the spinal cord ;
and it is only by the examination of transverse and longi-
tudinal sections through the substance of the cord, such as
those so successfully made by Mr. Lockhart Clarke, that we
can obtain anything like a correct idea of the direction
taken by the fibres of the roots of the spinal nerves within
the cord. From the information afforded by such sections
it would appear, that of the root-fibres of the nerve which
enter the cord, some assume a transverse, others a longi-
tudinal direction : the fibres of the former pass horizontally
or obliquely into the substance of the cord, in which many
of them appear to become continuous with fibres entering
the cord from other roots; others pass into the columns of
the cord, while some perhaps terminate at or near the part
which they enter: of the fibres of the second set, which
usually first traverse a portion of the grey substance, some
pass upwards, and others, at least of the posterior roots,
turn downwards, but how far they proceed in either direc-
tion, or in what manner they terminate, are questions still
_ undetermined. It is probable that of these latter, many
constitute longitudinal commissures, connecting different
segments of the cord with each other; while others, pro-
bably, pass directly to the brain.

The general rule respecting the size of different parts of
the cord appears to be, that the size of each part bears a
direct proportion to the size and number of nerve-roots
given off from itself, and has but little relation to the size
or number of those given off below it. Thus the cord is
very large in the middle and lower part of its cervical
portion, whence arise the large nerve-roots for the forma-
tion of the brachial plexuses and the supply of the upper
extremities, and again enlarges at the lowest part of its

ORIGIN OF THE SPINAL NERVES. 493
dorsal portion and the upper part of its lumbar, at the
origins of the large nerves which, after forming the lum-
bar and sacral plexuses, are distributed to the lower
extremities. The chief cause of the greater size at these
parts of the spinal cord is increase in the quantity of grey
matter; for there seems reason to believe that the white
or fibrous part of the cord becomes gradually and pro-
gressively larger from below upwards, doubtless from the
addition of a certain number of upward passing fibres from
each pair of nerves.

It may be added, however, that there is no sufficient
evidence for the supposition that an uninterrupted con-
tinuity of nerve-fibres is essential to the conduction of
impressions on the spinal nerves to and from the brain :
such impressions may be as well transmitted through the
nerve-vesicles of the cord as by the nerve-fibres; and the
experiments of Brown-Séquard, again to be alluded to,
make it probable that the grey substance of the cord is the
only channel through which sensitive i impressions are con-
veyed to the brain.

The Nerves of the Spinal Cord consist of thirty-one pairs,
issuing from the sides of the whole length of the cord, their
number corresponding with the intervertebral foramina
through which they pass. Each nerve arises by two roots,

an anterior and posterior, the latter being the larger. The ,

roots emerge through separate apertures of the sheath
of dura mater surrounding the cord; and directly after
their emergence, where the roots lie in the intervertebral
foramen, a ganglion is found on the posterior root. The
anterior root lies in contact with the anterior surface of
the ganglion, but none of its fibres intermingle with those
in the ganglion. But immediately beyond the ganglion
the two roots coalesce, and by the mingling of their fibres
form a compound or mixed spinal nerve, which, after
issuing from the intervertebral canal, divides into an

(
}

494. THE NERVOUS SYSTEM.

anterior and posterior branch, each containing fibres from
both the roots (fig. 141).

According to Kolliker the Deity’ root-fibres of the
cord enter into no connection with the nerve-corpuscles in
the ganglion, but pass directly through, in one or more
bundles, which are collected into a trunk beyond the gan-
glion, and then join the motor root. From most, if not all,
of the ganglionic corpusclés, one or two, rarely more,
nerve-fibres arise and pass out of the ganglion, in a peri-
pheral direction, in company with the posterior root-fibres
of the cord. Each spinal ganglion, therefore, is to be
regarded as a source of new nerve-fibres, which Kélliker

) names ganglionic fibres.. The destination of these fibres is

7

not yet determined: probably they pass especially into the
vascular branches of the nerves which they accompany.
The anterior root of each spinal nerve arises by nume-
rous separate and converging fasciculi from the anterior
column of the cord; the posterior root by more numerous
parallel fasciculi, from the posterior column, or, rather,
from the posterior part of the lateral column; for if a
fissure be directed inwards from the groove between the
middle and posterior columns, the posterior roots will
remain attached to the former. The anterior roots of each
spinal nerve consist exclusively of motor fibres; the
posterior as exclusively of sensitive fibres. For the know-
ledge of this important fact, and and much of the consequent
progress of the physiology of the nervous system, science
is indebted to Sir Charles Bell. The fact is proved m
various ways. Division of the anterior roots of one or
more nerves is followed by complete loss of motion in the
parts supplied by the fibres of such roots; but the sensa-
tion of the same parts remains perfect. Division of the
posterior roots destroys the sensibility of the parts supplied
by their fibres, while the power of motion continues unim-
paired. Moreover, irritation of the ends of the distal
portions of the divided anterior roots of a nerve excites

FUNCTIONS OF THE SPINAL CORD. 495

muscular movements ; irritation of the ends of the proximal
portions, which are still in connection with the cord, is
followed by no effect. Irritation of the distal portions of
the divided posterior roots, on the other hand, produces no
muscular movements and no manifestation of pain; for, as
already stated, sensitive nerves convey impressions only
towards the nervous centres : but irritation of the proximal
portions of these roots elicit signs of intense suffering.
Occasionally, under this last irritation, muscular move-
ments also ensue; but these are either voluntary, or the
result of the irritation being reflected from the sensitive to
the motor fibres. Occasionally, too, irritation of the distal
ends of divided anterior roots elicits signs of pain, as well
as producing muscular movements: the pain thus excited
is probably the result of cramp (Brown-Séquard).

As an example of the experiments of which the preced-
ing paragraph gives a summary account, this may be
mentioned: Ifin a frog the three posterior roots of the
nerves going to the hinder extremity be divided on the left
side, and the three anterior roots of the corresponding
nerves on the right side, the left extremity will be deprived
of sensation, the right of motion. If the foot of the right
leg, which is still endowed with sensation but not with the
power of motion, be cut off, the frog will give evidence of
feeling pain by movements of all parts of the body except
the right leg itself, in which he feels the pain. If, on the
contrary, the foot of the left leg, which has the power
of motion, but is deprived of sensation, is cut off, the frog

does not feel it, and no movement follows, except the
- twitching of the muscles irritated by cutting them or their
tendons.

Functions of the Spinal Cord.

The spinal cord manifests all the properties already
assigned to nerve centres (see p. 483).
1. It is capable of conducting impressions, or states of

490 THE NERVOUS SYSTEM.

nervous excitement. Through it the impressions made
upon the peripheral extremities or other parts of the spinal
sensitive nerves are conducted to the brain, where alone
they can be perceived by the mind. Through it, also, the
stimulus of the will, applied to the brain, is capable of
exciting the action of the muscles supplied from it with
motor nerves. And forall these conductions of impressions
to and fro between the brain and the spinal nerves, the
perfect state of the cord is necessary ; for when any part

of it is destroyed, and its communication with the brain is |

interrupted, impressions on the sensitive nerves given off
from it below the seat of injury, cease to be propagated to
the brain, and the mind loses the power of voluntarily
exciting the motor nerves proceeding from the portion of
cord isolated from the brain.

Illustrations of this are furnished by various examples
of paralysis, but by none better than by the common para-
plegia, or loss of sensation and voluntary motion in the
lower part of the body, in consequence of destructive
disease or injury of a portion, including the whole thick-
ness, of the spinal cord. Such lesions destroy the com-
munication between the brain and all parts of the spinal
cord below the seat of injury, and consequently cut off
from their connection with the mind the various organs
supplied with nerves issuing from those parts of the cord.
But if this lower portion of the cord preserves its integrity,
the various parts of the body supplied with nerves from it,
though cut off from the brain, will nevertheless be subject
to the influence of the cord, and, as presently to be shown,
will indicate its other powers as a nervous centre.

From what has been already said, it will appear probable
that the conduction of impressions along the cord is effected
(at least, for the most part) through the grey substance,
i.e., through the nerve-corpuscles and filaments connecting
them. But there is reason to believe that all parts of the
cord are not alike able to conduct all impressions; and

Fe el-a F eee aa ne ee

FUNCTIONS OF THE SPINAL CORD. 497

that, rather, as there are separate nerve-fibres for motor
and for sensitive impressions, so in the cord, separate and
determinate parts serve to conduct always the same kind
of impression.

The important and philosophical labours of Dr. Brown-

| Fig. 142.*

3
°
a—<e
i <x
ra SY

Lend

nme,
*».

Pd

* The above diagram (after Brown-Séquard) represents the decus-
sation of the conductors for voluntary movements, and those for
sensation : @ 7, anterior roots and their continuations in the spinal
cord, and decussation at the lower part of the medulla oblongata, m 0 ;
p 7’, the posterior roots and their continuation and decussation in the
spinal cord ; g g, the ganglions of the roots. The arrows indicate the
direction of the nervous action; 7, the right side; 7, the left side.
I, 2, 3, indicate places of alteration in a lateral half of the spino-
cerebral axis, to show the influence on the two kinds of conductors,
resulting from section of the cord at any one of these three places.

K

498 _ THE NERVOUS SYSTEM.

Séquard have cast much new light on all relating to
the functions of the spinal cord. It is not possible to
do justice to these investigations in any summary, how-
ever lengthy and complete: the whole series (delivered
in lectures at the College of Surgeons) must be
read and studied. An attempt will be made here to
point out only the principal conclusions deducible from
them.

a. Sensitive impressions, conveyed to the spinal cord by
root-fibres of the posterior nerves are not conducted to the
brain by the posterior columns of the cord, as hitherto has
been generally supposed, but pass through them into the
central grey substance, by which they are transmitted to
the brain (fig. 142).

b. The impressions thus conveyed to the grey substance
do not pass up to the brain along that half of the cord
corresponding to the side from which they have been
received, but, almost immediately after entering the cord,
cross over to the other side, and along it are transmitted
to the brain. There is thus, in the cord itself, a complete
decussation of sensitive impressions brought to it; so that
division or disease of one posterior half of the cord is
followed by lost sensation, not in parts on the correspond-
ing, but in those of the opposite side of the body.

c. The various sensations of touch, pain, temperature,
and muscular contraction, are probably conducted along
separate and distinct sets of fibres. All, however, with
the exception of the last named, undergo decussation in the
spinal cord, and along it are transmitted to the brain by
the grey matter.

d. The posterior columns of the cord appear to have a
great share in reflex movements, and this is the principal
cause of the peculiar kind of paralysis so often observed in
disease of these columns.

e. Impulses of the will, leading to voluntary contractions
of muscles, appear to be transmitted principally along the

x

CONDITION OF THE SPINAL CORD. 499

anterior columns, and the contiguous grey matter of the
cord.

jf. Decussation of motor impulses occurs, not in the

spinal cord, as is the case with sensitive impressions, but,
as hitherto admitted, at the interior part of the medulla
oblongata. This decussation, however, does not take place,
as generally supposed, all along the median line, at the
base of the encephalon, but only at that portion of the
.anterior pyramids, which is continuous with the lateral
columns of the cord. Hence, the mandates of the will,
having made their decussation, first enter the cord by the
lateral tracts and adjoining grey matter, and then pass to
the anterior columns and to the grey matter associated
with them. Accordingly, division of the anterior pyramids,
at the point of decussation, is followed by paralysis of
motion in all parts below; while division of the olivary
bodies, which constitute the true continuations of the
anterior columns of the cord, appears to produce very
little paralysis. Disease or division of any part of the
-cerebro-spinal axis above the seat of decussation is followed,
as well-known, by impaired or lost power of motion on
the opposite side of the body; while a like injury inflicted
below this part, induces similar paralysis on the corre-
sponding side.

2. In the second place, the spinal cord as a nerve-
centre, or rather as an aggregate of many nervous centres,
has the power of communicating impressions in the several
ways already mentioned (p. 485).

Examples of the transference and radiation of impressions
in the cord have been given; and that the transference at
least takes place in the cord, and not in the brain, is nearly
proved ky the case of pain felt in the knee and not in the
hip, in diseases of the hip; of pain felt in the urethra or
glans penis, and not in the bladder, in calculus; for, if
both the primary and the secondary or transferred impres-

sions were in the brain, both should be always felt. Of
KK 2

a
—

500 THE NERYOUS SYSTEM.

radiations of impressions, there are, perhaps, no means—
of deciding whether they take place in the spinal cord or
in the brain; but the analogy of the cases of transference
makes it probable that the communication is, in this also,
effected in the cord.

The power, as a nerve-centre, of communicating im~
pressions from sensitive to motor, or, more strictly, from
centripetal to centrifugal nerve-fibres, is what is usually
discussed as the reflex function of the spinal cord. Its
general mode cf action, its general though incomplete —
independence of consciousness and of the will, and the
conditions necessary for its perfection, have been already
stated. These points, and the extent to which the power
operates in the production of the natural reflex movements.
of the body, have now to be further illustrated. They
will be described in terms adapted to the general rules of
reflection of impressions in nervous centres, avoiding all
such terms as might seem to imply that the power of the
spinal cord in reflecting, is different in kind from that of
all other nervous centres,

The occurrence of movements under the influence of the
spinal cord, and independent of the will, is well exemplified.
in the acts of swallowing, in which a portion of food
carried by voluntary efforts into the fauces, is conveyed by
successive involuntary contractions of the constrictors of
the pharynx and muscular walls of the csophagus into.
the stomach. These contractions are excited by the stimu-
lus of the food on the centripetal nerves of the pharynx
and cesophagus being first conducted to the spinal cord
and medulla oblongata, and thence reflected through the
motor nerves of these parts. All these movements of the
pharynx and cesophagus are involuntary; the will cannot
arrest them or modify them; and though the mind has a
certain consciousness of the food passing, which becomes
less as the food passes further, yet that this is not neces-
sary to the act of deglutition, is shown by its occurring

REFLEX FUNCTION OF THE SPINAL CORD 5Or

when the influence of the mind is completely removed; as
when food is introduced into the fauces or pharynx during
a state of complete coma, or in a brainless animal.

So also, for example, under the influence of the spinal
cord, the involuntary and unfelt muscular contraction of
the sphincter ani is maintained when the mind is com-
pletely inactive, as in deep sleep, but ceases when the
lower part of the cord is destroyed, and cannot be main-

- tained by the will.

The independence of the mind manifested by the reflect-
ing power of the cord, is further shown in the perfect
occurrence of the reflex movements when the spinal cord
and the brain are disconnected, as in decapitated animals,
and in cases of injuries or diseases so affecting the spinal
cord as to divide or disorganize its whole thickness at any
part whose perfection is not essential to life. Thus, when
the head of a lizard is cut off, the trunk remains standing
on the feet, and the body writhes when the skin is irritated.
If the animal be cut in two, the lower portion can be ex-
cited to motion as well as the upper portion: the tail may
be divided into several segments, and each segment, in
which any portion of spinal cord is contained, contracts on
the slightest touch ; even the extremity of the tail moves
as before, as soon asitis touched. All the portions of the
animal in which these movements can be excited, contain
some part of the spinal cord; and it is evidently the cause
of the motions excited by touching the surface; for they
cannot be excited in parts of the animal, however large, if
no part of the cord is contained in them. Mechanical irri-
tation of the skin excites not the slightest motion in the
leo when it is separated from the body; yet the extremity
of the tail moves as soon as itis touched. The same power
of the spinal cord in reflecting impressions will cause an
ee], or a frog, or any other cold-blooded animal, to move
along after it is deprived of its head, and when, however
much the movements may indicate purpose, if is not

502 THE NERVOUS SYSTEM.

probable that consciousness or will has any share in
them. And so, in the human subject, or any warm-
blooded animal, when the cord is completely divided ©
across, or so diseased at some part that the influence
of the mind cannot be conveyed to the parts below it,
the irritation of any part of the surface supplied by.
nerves given off from the cord below the seat of injury,
is commonly followed by spasmodic and irregular reflex
movements, even though in the healthy state of the cord,
such involuntary movements could not be excited-when
the attention of the mind was directed to the irritating
cause.

In the fact last mentioned, is an illustration of an impor-
tant difference between the warm-blooded and the lower
animals, in regard to the reflecting power of the spinal cord
(or its homologue in the Invertebrata), and the share which
it and the brain have, respectively, in determining the
several natural movements of the body. When, for ex-
ample, a frog’s head is cut off, the limbs remain in, or
assume, a natural position; resume it when disturbed; and
when the abdomen or back is irritated, the feet are moved
with the manifest purpose of pushing away the irritation.
It is as if the mind of the animal were still engaged in
the acts.* But, in division of the human spinal cord, the
lower extremities fall into any position that their weight
and the resistance of surrounding objects combine to give
them; if the body is irritated, they do not move towards
the irritation; and if themselves are touched, the conse-
quent movements are disorderly and purposeless. Now, if

* The evident adaptation and purpose in the movements of the cold-
blooded animals, have led some to think that they must be conscious
and capable of will without their brains. But purposive movements
are no proof of consciousness or will in the creature manifesting them.
The movements of the limbs of headless frogs are not more purposive
than the movements’ of our own respiratory muscles are; in which we |
know that neither will nor consciousness is at all times concerned.

REFLEX FUNCTION OF THE SPINAL CORD. 503

we are justified by analogy in’ assuming that the will of
the frog cannot act more than the will of man, through
the spinal cord separated from the brain, then it must be
admitted that many more of the natural and purposive
movements of the body can be performed under the sole
influence of the cord in the frog than in man; and what
is true in the instance of these two species, is generally
true also of the whole class of cold-blooded, as distinguished
from warm-blooded, animals. It may not, indeed, be
assumed that the acts of standing, leaping, and other
movements, which decapitated cold-blooded animals can
perform, are also always, in the entire and healthy state,
performed involuntarily, and under the sole influence of
the cord; but it is probable that such acts may be, and
commonly are, so performed, the higher nerve-centres
of the animal having only the same kind of influence in
modifying and directing them, that those of man have in
modifying and directing the movements of the respiratory
muscles.

The fact that such movements as are produced by irri-
tating the skia of the lower extremities in the human
subject, after division or disorganization of a part of the
spinal cord, do not follow the same irritation when the
mind is active and connected with the cord through the
brain, is, probably, due to the mind ordinarily perceiving
the irritation and instantly controlling the muscles of the
irritated and other parts; for, even when the cord is per-
fect, such involuntary movements will often follow irritation,
if it be applied when the mind is wholly occupied. When,
for example, one is anxiously thinking, even slight stimuli
will produce involuntary and reflex movements. So, also,
during sleep, such reflex movements may be observed when
the skin is touched or tickled ; for example, when one touches
with the finger the palm of the hand of a sleeping child,
the finger is grasped—the impression on the skin of the
palm producing a reflex movement of the muscles which

504 THE NERVOUS SYSTEM.

close the hand. But when the child is awake, no such
effect is produced by a similar touch.

On the whole, it may, from these and like facts, be con-
cluded that the proper reflex acts, performed under the
influence of the reflecting power of the spinal cord, are
essentially independent of the brain, and may be performed
perfectly when the brain is separated from the cord : * that
these include a much larger number of the natural and
purposive movements of the lower animals than of the
warm-blooded animals and man: and that over nearly all
of them the mind may exercise, through the brain, some
control; determining, directing, hindering, or modifying
them, either by direct action or by its power over associated
muscles. .

In this fact, that the reflex movements from the cord’
may be perfectly performed without the intervention of
consciousness or will, yet are amenable to the control of
the will, we may see their admirable adaptation to the
well-being of the body. Thus, for example, the respiratory
movements may be performed while the mind is, in other
things, fully occupied, or in sleep powerless; yet in an
emergency, the mind can direct and strengthen them: and
it can adapt them to the several acts of speech, effort, ete.
Being, for ordinary purposes, independent of the will and
consciousness, they are performed perfectly, without expe-
rience or education of the mind; yet they may be employed
for other and extraordinary uses when the mind wills, and
so far as it acquires power over them. Being commonly
independent of the brain, their constant continuance does
not produce weariness; for it is only in the brain that it or
any other sensation can be perceived.

The subjection of the muscles to both the spinal cord

* Reflex movements, occurring quite independently of sensation, are
generally called excito-motor ; those which are guided or accompanied
by sensation, but not to the extent of a distinct perception or intel-
lectual process, are termed sensori-motor.

REFLEX FUNCTION OF THE SPINAL CORD. 505

and the brain, makes it difficult to determine in man what
movements or what share in any of them can be assigned
to the reflecting power of the cord. The fact that after
division or disorganization of a part of the cord, move-
ments, and even forcible though purposeless ones, are pro-
duced in the lower limbs when the skin is irritated, proves
that the spinal cord can reflect a stimulus to the action of
the muscles that are, naturally, most under the control of
_ the will; and it is, therefore, not improbable that, for even
the involuntary action of those muscles, when the cord is per-
fect, it may supply the nervous stimulus, and the will the
direction. As instances in which it supplies both stimulus
and direction, that is, both excites and determines the com-
bination of muscles, may be mentioned the acts of the abdo-
minal muscles in vomiting and voiding the contents of the
bladder and rectum; in both of which, though, after the
period of infancy, the mind may have the power of post-
poning or modifying the act, there are all the evidences of
reflex action; namely, the necessary precedence of a sti-
mulus, the independence of the will, and, sometimes of
consciousness, the combination of many muscles, the per-
fection of the act without the help of education or experi-
ence, and its failure or imperfection in disease of the lower
part of the cord. The emission of semen is equally a reflex
act governed by the spinal cord: the irritation of the glans
penis conducted to the spinal cord, and thence reflected,
excites the successive and co-ordinate contractions of the
muscular fibres of the vasa deferentia and vesiculee semi-
nales, and of the accelerator urinze and other muscles of
the urethra; and a forcible expulsion of semen takes place,
over which the mind has little or no control, and which, in
eases of paraplegia, may be unfelt. The erection of the
penis, also, as already explained (p. 185), appears to be in
part the result of a reflex contraction of the muscles by
which the veins returning the blood from the penis are
compressed. Irritation of the vagina in sexual intercourse

506 THE NERVOUS SYSTEM.

\.

appears also to be propagated to the spinal cord, and thence
reflected to the motor nerves supplying the Fallopian tubes.
The involuntary action of the uterus in expelling its con-
_ tents during parturition, is also of a purely reflex kind,
dependent in part upon the spinal cord, though in part
also upon the sympathetic system: its independence of the
brain being proved by cases of delivery in paraplegic
women, and now more abundantly shown in the use of
chloroform. }

Besides these acts regularly performed under the influ-
ence of the reflecting power of the spinal cord, others are
manifested in accidents, such as the movement of the limbs
and other parts to guard the body against the effects of
sudden danger. When, for example, a limb is pricked or
struck, it is instantly and involuntarily withdrawn from the
instrument of injury; and the same preservative tendency
of the reflex power of the cord is shown in the outstretched
arms when falling forwards, and their reversed position
when falling backwards; the action, although apparently
voluntary, being really, in most cases, only an instance of
reflex action.

To these instances of spinal reflex action, some add yet
many more, including nearly all the acts which seem to be
performed unconsciously, such as those of walking, running,
writing, and the like: for these are really involuntary
acts. Itis true that at their first performances they are
- voluntary, that they require education for their perfection,
and are at all times so constantly performed in obedience
to a mandate of the will, that it is difficult to believe in
their essentially involuntary nature. But the will reaily
has only a controlling power over their performance; it can
hasten or stay them, but it has little or nothing to do with
the actual carrying out of the effect. And this is proved
by the circumstance that these acts can be performed with
complete mental abstraction: and, more than this, that the
endeavour to carry them out entirely by the exercise of the

REFLEX FUNCTION OF THE SPINAL CORD. 507

will is not only not beneficial, but positively interferes with
their harmonious and perfect performance. Anyone may
convince himself of this fact by trying to take each step as
a voluntary act in walking down stairs, or to form each
letter or word in writing by a distinct exercise of the will.

These actions, however, will be again referred to, when
treating of their possible connection with the functions of
the so-called sensory ganglia (p. 523).

The phenomena of spinal reflex actions in man are much
more striking and unmixed in cases of disease. In some of
these, the effect of a morbid irritation, or a morbid irri-
tability of the cord, is very simple; as when the local
irritation of sensitive fibres, being propagated to the
spinal cord, excites merely local spasms,—spasms, namely,
of those muscles, the motor fibres of which arise from the
same part of the spinal cord as the sensitive fibres that are
irritated. Of such a case we have instances in the invol-
untary spasmodic contraction of muscles in the immediate
neigbbourhood of inflamed joints; and numerous other
examples of a like kind might be quoted.

In other instances, in which we must assume that the
cord is morbidly more irritable, i.¢., apt. to issue more
| nervous force than is proportionate to the stimulus applied
- to it, a slight impression on a sensitive nerve produces ex-
:

J

tensive reflex movements. This appears to be the condition
in tetanus, in which a slight touch on the skin may throw
the whole body into convulsion. A similar state is induced
by the introduction of strychnia, and, in frogs, of opium,
into the blood; and numerous experiments on frogs thus
made tetanic, have shown that the tetanus is wholly uncon-
nected with the brain, and depends on the state induced in
the spinal cord.

It may seem to have been implied that the spinal cord, as
a single nervous centre, reflects alike from all parts all the
impressions conducted to it. But it is more probable that

a err

508 THE NERVOUS SYSTEM.

it should be regarded as a collection of nervous centres”
united in a continuous column. This is made probable by
the fact that segments of the cord may act as distinct ner-
vous centres, and excite motions in the parts supplied with
nerves given off from them; as well as by the analogy of
certain cases in which the muscular movements of single
organs are under the control of certain circumscribed por-
tions of the cord. Thus Volkmann has shown that the
rhythmical movements of the anterior pair of lymphatic
hearts in the frog depend upon nervous influence derived
from the portion of spinal cord corresponding to the third
vertebra, and those of the posterior pair on influence sup-
_plied by the portion of cord opposite the eighth vertebra.
The movements of the heart continue, though the whole of
the cord, except the above portions, be destroyed; but on
the instant of destroying either of these portions, though
all the rest of the cord be untouched, the movements of
the corresponding hearts cease. What appears to be thus
‘proved in regard to two portions of the cord, may be in-
ferred to prevail in other portions also; and the inference
is reconcilable with most of the facts known concerning
the physiology and comparative anatomy of the cord.

The influence of the spinal cord on the sphincter ani has
been already mentioned (p. 501). It maintains this muscle
in permanent contraction, so that, except in the act of defeca-
tion, the orifice of the anus is always closed. This influence
of the cord resembles its common reflex action in being in-
voluntary, although the will can act on the muscle to make
it contract more or to permit its dilatation, and in that the
constant action of the muscle is not felt, nor diminished in
sleep, nor productive of fatigue. But the act is different
from ordinary reflex acts in being nearly constant. In
this respect it resembles that condition of muscles which —
has been called tone,* or passive contraction; in a state in

* This kind of tone must be distinguished from that mere firmness

— Pe 6

——

oe tae

a
~"s

Tae ST

STRUCTURE OF THE MEDULLA OBLONGATA. 509

which they always appear to be when not active in health,
and in which, though called inactive, they appear to be in
slight contraction, and certainly are not relaxed, as they
are long after death, or when the spinal cord is destroyed.
This tone of all the muscles of the trunk and limbs seems
to depend on the spinal cord, as the contraction of the
sphincter ani does. If an animal be killed by injury or
removal of the brain, the tone of the muscles may be felt,
and the limbs feel firm as during sleep; but if the spinal
cord be destroyed, the sphincter ani relaxes, and all the

- muscles feel loose, and flabby, and atonic, and remain so

till the rigor mortis commences.

THE MEDULLA OBLONGATA,

Its Structure.

The medulla oblongata is a mass of grey and white
nervous substance partly contained within the cavity of the
cranium,—forming a portion of the cephalic prolongation
of the spinal cord and connecting it with the brain. The
grey substance which it contains is situated in the interior,
and variously divided into masses and laminz by the white
or fibrous substance which is arranged partly in external
columns, and partly in fasciculi traversing the central grey
matter. The medulla oblongata is larger than any part of
the spinal cord. Its columns are pyriform, enlarging as
they proceed towards the brain, and are continuous with
those of the spinal cord.

Each half of the medulla, therefore, may be divided into
three columns or tracts of fibres, continuous with the three

and tension which it is customary to ascribe, under the name of tone,
to all tissues that feel robust and not flabby, as well as to muscles.
The tone peculiar to muscles has in it a degree of vital contraction :
that of other tissues is only due to their being well nourished, and
therefore compact and tense.

510 THE NERVOUS SYSTEM.
tracts of which each half of the spinal cord is made up.
The columns are more prominent than those of the spinal
cord, and separated from each other by deeper grooves. The
anterior, continuous with the anterior columns of the cord,
are called the anterior pyramids; the posterior, continuous
with the posterior columns of the cord, are called the restiform

Fig. 143.* Fig. 144.F

Oy

* Fig. 143. View of the anterior surface of the pons Varolii, and
medulla oblongata. a, a, anterior pyramids ; 0, their decussation ; ¢, ¢,
olivary bodies; d@, d, restiform bodies ; ¢, arciform fibres; jf, fibres
described by Solly as passing from the anterior column of the cord to
the cerebellum ; g, anterior column of the spinal cord; h, lateral
column ; p, pons Varolii ; ¢, its upper fibres ; 5, 5, roots of the fifth
pair of nerves. ~

+ Fig. 144. View of the posterior surface of the pons Varolii, cor-
pora quadrigemina, and medulla oblongata, The peduncles of the
cerebellum are cut short at the side. a, a, the upper pair of cor-
pora quadrigemina ; 0, 6, the lower; jf, f, superior peduncles of the
cerebellum ; c, eminence connected with the nucleus of the hypoglossal
nerve ; ¢, that of the glosso-pharyngeal nerve ; 7, that of the vagus
nerve; d, d, restiform bodies; p, p, posterior pyramids ; v, v, groove
in the middle of the fourth ventricle, ending below in the Sion core
scriptorius ; 7, 7, roots of the auditory nerves.

STRUCTURE OF THE MEDULLA OBLONGATA. 511

bodies ; and the lateral, continuous with thelateral columns
of the cord, are named simply from their position. On the
fibres of the lateral column of each side, near its upper
part, is a small oval mass containing grey matter, and
named the olivary body; and at the posterior part of the
restiform column, immediately on each side of the posterior
median groove, a small tract is marked off by a slight
groove from the remainder of the restiform body, and called
the posterior pyramid. The restiform columns, instead of
remaining parallel with each other throughout the whole
of the medulla oblongata, diverge near its upper part,
and by thus diverging, lay open, so to speak, a space called
the fourth ventricle, the floor of which is formed by the
grey matter of the interior of the medulla, by this diverg-
ence exposed.

On separating the anterior pyramids, and looking into
the groove between mink, some decussating fibres can be
| plainly seen.

Distribution of the Fibres of the Medulla Oblongata.

The anterior pyramid of each side, although mainly com-
posed of continuations of the fibres of the anterior columns
of the spinal cord, receives fibres from the lateral columns,
both of its own and the opposite side; the latter fibres
forming almost entirely those decussating strands before
mentioned, which are seen in the groove between the
anterior pyramids.

Thus composed, the anterior pyramidal fibres proceed-
ing onwards to the brain are distributed in the following
manner :—I. The greater part pass on through the pons
to the cerebrum.* A portion of the fibres, however, run-

.* The expressions “continuous fibres,” and the like, appear to be
usually understood as meaning that certain primitive nerve-fibres pass
without interruption from one part to another. But such continuity.
of primitive fibres through long distances in the nervous centres is

|

512 THE NERYOUS SYSTEM.

ning apart from the others, joins some fibres from the
olivary body, and unites with them to form what is called
the olivary fasciculus or fillet. 2. A small tract of fibres
proceeds to the cerebellum.

The lateral column on each side of the medulla, in pro--
ceeding upwards, divides into three parts, outer, inner,
and middle, which are thus disposed of :—1. The outer
fibres go with the restiform tract to the cerebellum. 2. The
middle decussate across the middle line with their fellows,
and form a part of the anterior pyramid of the opposite —
side. 3. The inner pass on to the cerebrum along the floor
of the fourth ventricle, on each side, under the name of the
fasciculus teres.

The fibres of the restiform body receive some small con-
tributions from both the lateral and anterior columns of
the medulla, and proceed chiefly to the cerebellum, but
that small part behind, called posterior pyramid, is con-
tinued on with the fasciculus teres of each side along the

floor of the fourth ventricle to the cerebrum.

As in structure, so also in the general endowments of
their several parts, there is, probably, the closest analogy
between the medulla oblongata and the spinal cord. The
difference between them in size and form appears due,
chiefly, first, to the divergence, enlargement, and decussa-
tion of the several columns, as they pass to be connected
with the cerebellum or the cerebrum ; and, secondly, to the
insertion of new quantities of grey matter in the olivary
bodies and other parts, in adaptation to the higher office

very far from proved, The apparent continuity of fasciculi (which is
all that dissection can yet trace) is explicable on the supposition that
many comparatively short fibres lie parallel, with the ends of each
inlaid among many others. In such a case, there would be an apparent
continuity of fibres; just as there is, for example, when one untwists
and picks out a long cord of silk or wool, in which each fibre is short,
and yet each fasciculus appears to be continued through the whole
cord,

a

aia Ne gl el a "

FUNCTIONS OF THE MEDULLA OBLONGATA. 513

and wider range of influence which the medulla oblongata
as a nervous centre exercises.

Functions of the Medulla Oblongata.

In its functions the medulla oblongata differs from the
spinal cord chiefly in the importance and extent of the
actions that it governs. Like the cord, it may be regarded
first, as conducting impressions, in which office it has a
wider extent of function than any other part of the nervous
system, since it is obvious that all impressions passing to
and fro between the brain and the spinal cord .and all
nerves arising below the pons, must be transmitted through
it. The decussation of part of the fibres of the anterior

pyramids of the medulla oblongata explains the pheno- |
mena of cross-paralysis, as it is termed, ¢.¢., of the loss of |

motion in cerebral apoplexy, being always on the side
opposite to that on which the effusion of blood has taken
place. Looking only to the anatomy of the medulla
oblongata, it was not possible to explain why the loss of
sensation also is on the side opposite the injury or
disease of the brain: for there is no evidence of a
decussation of posterior fibres like that which ensues
among the anterior fibres of the medulla oblongata.
But the discoveries of Brown-Séquard have shown that
the crossing of sensitive impressions occurs in the spinal
cord (see p. 498).

The functions of the medulla oblongata as a nerve-centre
seem to be more immediately important to the maintenance
of life than those of any other part of the nervous system,
since from it alone, or in chief measure, appears to be
reflected the nervous force necessary for the performance of
respiration and deglutition. It has been proved by repeated
experiments on the lower animals that the entire brain
may be gradually cut away in successive portions, and yet

life may continue for a considerable time, and the respiratory
i) re

514 THE NERVOUS SYSTEM.

movements be uninterrupted. Life may also continuewhen
the spinal cord is cut away in successive portious from
below upwards as high as the point of origin of the phrenic
nerve, or in animals without a diaphragm, such as birds or
reptiles, even as high as the medulla oblongata. In Am-
phibia, these two experiments have been combined: the
brain being all removed from above, and the cord from
below ; and so long ‘as the medulla oblongata was intact,
respiration and life were maintained. But if, in anyanimal,
the medulla oblongata is wounded, particularly if it is
wounded [in its central part, opposite the origin of the
pneumogastric nerves, the respiratory movements cease,
and the animal dies as if asphyxiated. And this effect
ensues even when all parts of the nervous system, except
the medulla oblongata, are left intact.

Injury and disease in men prove the same as these ex-
periments on animals. Numerous instances are recorded
in which injury to the human medulla oblongata has
produced instantaneous death; and, indeed, it is through
injury of it, or of the part of the cord connecting it with
the origin of the phrenic nerve, that death is commonly
produced in fractures and diseases with sudden displace-
ment of the upper cervical vertebree.

The centre whence the nervous force for the pivdusiton
of combined respiratory movements appears to issue is in
the interior of that part of the medulla oblongata from
which the pneumogastric nerves arise; for-with care the
medulla oblongata may be divided to within a few lines of
this part, and its exterior may be removed without the
stoppage of respiration; but it immediately ceases when
this part is invaded. This is not because the integrity of
the pneumogastric nerves is essential to the respiratory
movements; for both these nerves may be divided without
more immediate effect than a retardation of these move-
ments. The conclusion, therefore, may safely be, that
this part of the medulla oblongata is the nervous centre

FUNCTIONS OF THE MEDULLA OBLONGATA. 515

whereby the impulses NEE he the respiratory move-
ments are reflected.

The power by which the medulla oblongata governs and
combines the action of various muscles for the respiratory
movements, is an instance of the power of reflexion, which
it possesses in common with all nervous centres. Its
general mode of action, as well as the degrees to which
the mind may take part in respiration, and the number
of nerves and muscles which, under the governance of the
medulla oblongata, may be combined in the forcible respi-
ratory movements, have been already briefly described (see
p. 225 et seq.). That which seems most peculiar in this
‘centre of respiratory action is its wide range of connection,
the number of nerves by which the centripetal impression
to excite motion may be conducted, and. the number and
‘distance of those through which the motor impulse may be
directed. The principal centripetal nerves engaged in
respiration are the pneumogastric, whose branches supply-
‘ing the lungs appear to convey the most acute impression
of the ‘‘necessity of breathing.”” When they are both
divided, the respiration becomes slower (J. Reid), as if the
necessity were less acutely felt: but it does not cease, and
therefore other nerves besides them must have the power
of conducting the like impression. The experiments of
Volkmann make it probable that all centripetal nerves —
possess if in some degree, and that the existence of imper-
fectly aerated blood in contact with any of them acts as a
stimulus, which, being conveyed to the medulla oblongata,
is reflected to the nerves of the respiratory muscles: so
that respiratory movements do not wholly cease so long as
any centripetal nerves, and any nerve supplying muscles
of respiration, are both in continuous connection with the
respiratory centre of the medulla oblongata. The circulation
of imperfectly aerated blood in the medulla oblongata itself
may also act as a stimulus, and react through this nerve-
centre on the nerves which supply the inspiratory muscles,

LL 2

516 THE NERVOUS SYSTEM,

The wide extent of connection which belongs to the
medulla oblongata as the centre of the respiratory move-
ments, is further shown by the fact that impressions by
mechanical and other ordinary stimuli, made on many
parts of the external or internal surface of the body, may
induce respiratory movements. Thus involuntary respira-
tions are induced by the sudden contact of cold with any
part of the skin, as in dashing cold water into the face.
Irritation of the mucous membrane of the nose produces,
sneezing. Irritation in the pharynx, cesophagus, stomach,
or intestines, excites the concurrence of the respiratory
movements to produce vomiting. Violent irritation in the
rectum, bladder, or uterus, gives rise to a concurrent action
of the respiratory muscles, so as to effect the expulsion of
the feeces, urine, or foetus.

The medulla oblongata appears to be the centre whence:
are derived the motor impulses enabling the muscles of
the palate, pharynx, and cesophagus, to produce the suc-
cessive co-ordinate and adapted movements necessary to.
the act of deglutition (see Dp. 263). This is proved by the

| persistence of swallowing in some of the lower animals
| after destruction of the cerebral hemispheres and cerebel-
' lum; its existence in anencephalous monsters; the power
of swallowing possessed by Mmarsupial embryoes before the
WA“&4%-brain is developed; and by the complete arrest of the
power of swallowing when the medulla oblongata is injured
in experiments. But the reflecting power herein exercised
by the medulla oblongata is of a much simpler and more
restricted kind than that exercised in respiration; it is,
indeed, not more than a simple instance of reflex action by
a segment of the spinal axis, receiving impressions for this
purpose from only a few centripetal nerves, and reflecting
them to the motor nerves of the same organ. The incident
or centripetal nerves in this case are the branches of the
glossopharyngeal, and, in a subordinate degree, those of
the fifth nerve, some of the branches of the suyerior laryn-

;
“
i

FUNCTIONS OF THE MEDULLA OBLONGATA. 517

geal nerve, which are distributed to the pharynx; and the
nerves through which the motor impressions to the fauces
and pharynx are reflected, are the pharyngeal branches of
the vagus, and, in subordinate degrees, or as supplying
muscles accessory to the movements of the pharynx, the
branches of the hypoglossal, facial, cervical, recurrent, and
fifth nerves. For the csophageal movements, so far as
they are connected with the medulla oblongata, the fila-
ments of the pneumogastric nerve alone, which contain
both afferent and efferent fibres, appear to be sufficient
{John Reid).

Though respiration and life continue while the medulla

oblongata is perfect and in connection with respiratory

nerves, yet, when all the brain above it is removed, there
is no more appearance of sensation, or will, or of any
mental act in the animal, the subject of the experiment,
than there is when only a spinal cord is left. The move-
ments are all involuntary and unfelt; and the medulla
oblongata has, therefore, no claim to be considered as an
organ of the mind, or as the seat of sensation or volun-
tary power. These ‘are connected with parts next to be
‘described.

It would appear that much of the reflecting power of
the medulla oblongata may be destroyed; and yet its
power in the respiratory movements may remain. Thus,
in patients completely affected with chloroform, the wink-
ing of the eye-lids ceases, and irritation of the pharynx
will not produce the usual movements of swallowing, or
the closure of the glottis (so that blood may run quietly
into the stomach, or even into the lungs); yet, with all
this, they may breathe steadily, and show that the power
of the medulla oblongata to combine in action all the
nerves of the respiratory muscles is perfect.

In addition to its influence over the functions of respira- |
tion and deglutition, the medulla oblongata appears to be
largely concerned also in the faculty of speech.

- 518 THE NERVOUS SYSTEM.

In the medulla oblongata appears to be seated also the
chief vaso-motor_nerve-centre (p. 576). From this arise
fibres which, passing down the spinal cord, issue with the
anterior roots of the spinal nerves, and enter the ganglia
and branches of the sympathetic, by which they are
conducted to the blood-vessels.

The influence which is exercised by the medulla ob-
longata, or, at least, by its irritation, on the formation of
sugar in the liver, has been referred to (p. 336).

STRUCTURE AND PHYSIOLOGY OF THE PONS YVAROLII,
CRURA CEREBRI, CORPORA QUADRIGEMINA, CORPORA
GENICULATA, OPTIC THALAMI, AND CORPORA STRIATA.

Pons Varolii—The meso-cephalon, or pons (v1, fig. 145),
is composed principally of transverse fibres connecting the
two hemispheres of the cerebellum, and forming its prin-
cipal commissure. But it includes, interlacing with these,
numerous longitudinal fibres which connect the medulla
oblongata with the cerebrum, and transverse fibres which
connect it with the cerebellum. Among the fasciculi of
nerve-fibres by which these several parts are connected,
the pons also contains abundant grey or vesicular sub-
stance, which appears irregularly placed among the fibres,
and fills up all the interstices.

The anatomical distribution of the fibres, both trans-
verse and longitudinal, of which the pons is composed, is
sufficient evidence of its functions as a conductor of im-
pressions from one part of the cerebro-spinal axis to
another. |

Concerning its functions as a nerve-centre, little or
nothing is certainly known.

Crura Cerebri.—The crura cerebri (111, fig. 145), are prin-
cipally formed of nerve-fibres, of which the inferior or more
superficial are continuous with those of the anterior pyra-

~~ =

ee Se aA CC

THE PONS VAROLII, — 519

midal tracts of the medulla oblongata, and the superior or |
deeper fibres with the lateral and posterior pyramidal tracts,
and with the olivary fasciculus. Besides these fibres from
the medulla oblongata, are others from the cerebellum and

some of the latter as well as a part of the fibres derived

from the lateral tract of the medulla oblongata, decussate
across the middle line.

* Fig. 145. Base of the brain (from Quain). 4.—1, superior longi-
tudinal fissure ; 2, 2’, 2”, anterior cerebral lobe ; 3, fissure of Sylvius,
between anterior and 4, 4’, 4", middle cerebral lobe; 5, 5’, posterior
lobe ; 6, medulla oblongata; the figure is in the right anterior pyra-
mid ; 7, 8, 9, 10, the cerebellum ; +, the inferior vermiform process.
The figures from J. to IX. are placed against the corresponding
cerebral nerves ; III. is placed on the right crus cerebri ; VI. and VII.
on the pons Varolii; X. the first cervical or suboccipital nerve.

520 THE NERVOUS SYSTEM.

On their upper part the crura cerebri bear three pairs:
of small ganglia, or masses of mingled grey and white
nerve-substance, namely, the corpora geniculata externa
and interna, and the corpora quadrigemina, or nates and testes.
And in their onward course to the cerebrum, the fibres of
each crus cerebri pass through two large ganglia, the optic
thalamus and corpus striatum, and in their substance come
into connection with variously-shaped masses and layers
of grey substance. Whether all the fibres of the crura
cerebri end in the grey matter of these two ganglia, while”
others start afresh from them to enter the cerebral hemi-
spheres; or whether some of the fibres of the crura pass
through them, while only a portion can be strictly said to
have their termination there, must remain at present
undecided; the. difficulties in the way of solving such an
anatomical doubt being at present insuperable.

Each crus cerebri contains among its fibres a mass of
vesicular substance, the locus niger, the nerve-corpuscles of
which abound in pigment-granules, and afford some of the
best instances of the caudate structure.
be regarded as, principally, poiddeline organs. - As nerve-
centres they are probably connected with the functions of
the third cerebral nerve, which arises from the locus niger,
and thy through which are directed the chief of the numerous
and complicated movements of the eyeball and iris.

From the result of vivisection it appears that when one
of the crura cerebri is cut across, the animal moves round
and round, rotating around a vertical axis from the injured
towards the sound side. Such movements, however, attend
the sections of other parts than the crura_ cerebri:
and as indications of the functions of these parts, the
results of such experiments have been hitherto almost
valueless.

Corpora Quadrigemina.—The corpora quadrigemina (from

FUNCTIONS OF THE SENSORY GANGLIA. 521
which, in function, the corpora geniculata are not distin-

Amphibia and fishes, and may be regarded as the prin-

guished), are the homologues of the optic lobes in in|

cipal nervous centres for the sense of sight. The experi-
ments of Flourens, Longet, and Hertwig, show that
removal of the corpora quadrigemina wholly destroys sae
power of seeing; and-diseases in which they are disor- |
ganized are usually accompanied with blindness. Atrophy
of them is also often a consequence of atrophy of the eyes.

Destruction of one of the corpora quadrigemina (or of
one optic lobe in birds), produces blindness of the oppo-

This loss of sight is the only apparent injury of
sensibility sustained by the removal of the corpora quad-
rigemina. The removal of one of them affects the move-
ments of the body, so that animals rotate, as after division
of the crus cerebri, only more slowly: but this is probably
due to giddiness and partial loss of sight. The more
evident and direct influence is that produced on the iris.
It contracts when the corpora quadrigemina are irritated :
it is always dilated when they are removed: so that they
may be regarded, in-some measure at least, as the nervous
centres governing its movements, and adapting them to:
the impressions derived from the retina through the optic
nerves and tracts.

. Concerning the functions, taken asa whole, discharged by
the olfactory and optic lobes, the grey substance of the pons,
the corpora striata and optic thalami (3, d, fig. 146), with
some other centres of grey matter not so distinct, such as the
grey matter on the floor of the fourth ventricle with which
the auditory nerve is connected, the most philosophical
theory is undoubtedly that which has been so ably enun-
ciated by Dr. Carpenter. He supposes these ganglia to
constitute the real sensorium ; that is to say, it is by means
of them that the mind becomes conscious of impressions

|

522 THE NERVOUS SYSTEM.

made on the organs or tissues with which (by means of
Fig. 146.*

* Fig. 146. Dissection of brain, from above, exposing the lateral,
fourth, and fifth ventricles, with the surroundiug parts (from Hirsch-
feld and Leveillé). 4.—a, anterior part, or genw of corpus callosum ;
b, corpus striatum ; 0’, the corpus striatum of left side, dissected so as
to expose its grey substance ; c, points by a line to the tenia semicu-
laris ; d, optic thalamus ; ¢, anterior pillars of fornix divided ; below
they are seen descending in front of the third ventricle, and between
them is seen part of the anterior commissure ; in front of the letter e
is seen the slit-like fifth ventricle, between the two lamine of the
septum lucidum ; f, soft or middle commissure ; g is placed in the pos-
terior part of the third ventricle ; immediately behind the latter are
the posterior commissure (just visible) and the pineal gland, the two
crura of which extend forwards along the inner and upper margins of
the optic thalami; % and z, the corpora quadrigemina ; %, superior
crus of cerebellum ; close to # is the valve of Vieussens, which has
been divided so as to expose the fourth ventricle; 7, hippocampus

;
}

THE CEREBELLUM. 523

nerve-fibres) they are in communication. Thus impres-
sions made on the optic nerve, or its expansion in the
retina, are conducted by the fibres of the optic nerve to
the ‘corpora quadrigemina, and through the medium of
these ganglia the mind becomes conscious of the impres-
sion made. And impressions on the filaments of the
olfactory or auditory nerve are in the same way perceived °
through the medium of the olfactory or auditory ganglia,
to which they are first conveyed. The optic thalami and
corpora striata probably have some function of a like kind
—perhaps in relation to ordinary sensation, but nothing is

_ certainly known regarding them,

Besides their functions, however, as media of communi-
cation between the mind and external objects, these sensory
ganglia, as they are termed, are probably the nerve-centres
by means of which those reflex acts are performed which
require either a higher combination of muscular acts than
can be directed. by means. of the medulla oblongata or
spinal cord alone, or on the other hand, such reflex actions
as require for their right performance the guidance of
sensation. Uvder this head are included various acts, as
walking, reading, writing, and the like, which we are
accustomed to consider voluntary, but which really are as
incapable of being performed by distinct. and definite acts
of the will as are those more simple movements of which
we are not conscious, and which, performed under the
guidance of the spinal cord or medulla oblongata alone,
we call simple reflex actions. It is true that in the per-
formance of such acts as those just-mentioned, a certain
exercise of the will is required at the commencement, but

that the carrying out of its mandates is essentially reflex

major and corpus fimbriatum, or tenia hippocampi ; m, hippocampus
minor ; ”, eminentia collateralis; o, fourth ventricle ; p, posterior
surface of medulla oblongata; 7, section of cerebellum ; s, upper part
of left hemisphere of cerebellum exposed by the removal of part of the
posterior cerebral lobe.

p24 THE NERVOUS SYSTEM.

and involuntary, anyone may convince himself by trying
to perform each individual movement concerned, strictly
as a voluntary act.

That such movements are reflex and essentially inde-
pendent—as regards their mere production—of the will,
there is no doubt: that the nerve-centres through which
such reflex actions are performed are the so-called sensory
ganglia, is, of course, only a theory which may or not be
confirmed by future investigations.

Besides their possible functions in the manner just men-
tioned, it is supposed that these sensory ganglia may be
the means of transmitting the impulses of the will to the
muscles, which act in obedience to it, and thus be the
centres of reflex action as well for impressions conveyed
downwards to them from the cerebral hemispheres, as for
impressions carried upwards to them by the different nerves
which preserve their connection with the organs of the
various senses.

STRUCTURE AND PHYSIOLOGY OF THE CEREBELLUM.

The cerebellum (7, 8, 9, 10, fig. 147) is composed of an
elongated central portion called the vermiform processes,
and two hemispheres. Each hemisphere is connected with
its fellow, not only by means of the vermiform processes,
but also by a bundle of fibres called the middle crus or
peduncle (the latter forming the greater part of the pons
Varolii), while a superior crus with the valve of Vieussens,
connects it with the cerebrum (fig. 147, 5,) and an inferior
crus (formed by the prolonged restiform body) connects it
with the medulla oblongata (3, fig. 147).

The cerebellum is composed of white and grey matter
like that of the cerebrum, but arranged after a different
fashion as shown in fig. 147. z

Besides the grey substances on the surface, however,
there is near the centre of the white substance of each

- “¢

er

FUNCTIONS OF THE CEREBELLUM. 525

hemisphere, a small capsule of grey matter called the

‘corpus dentatum (fig. 148, ed), resembling very closely the

corpus dentatum of the olivary body of the medulla oblon-
gata (fig. 148, 9).

The physiology of the cerebellum may be dotiaidared in
its relation to sensation, voluntary motion, and the instincts
or higher faculties of the mind. It is itself insensible to
irritation, and may be all cut away without eliciting signs

* Fig. 147. View of cerebellum in section and of fourth ventricle,
with the neighbouring parts (from Sappey after Hirschfeld and Le-
veillé). 1, median groove of fourth ventricle, ending below in the
calamus scriptorius, with the longitudinal eminences formed by the
Jfasciculi teretes one on each side; 2, the same groove, at the place
where the white streaks of the auditory nerve emerge from it to cross
the floor of the ventricle ; 3, inferior crus or penduncle of the cere-
bellum, formed by the restiform body ; 4, posterior pyramid ; above
this is the calamus scriptorius ; 5, superior crus of cerebellum, or pro-
cessus a cerebello ad cerebrum (or ad testes) ; 6, 6, fillet to the side of
the crura cerebri ; 7, 7, lateral grooves of the crura cerebri ; 8, corpora
quadrigemina.

/

526 | THE NERVOUS SYSTEM.

of pain (Longet). Yet, if any of its crura be touched, pain
is indicated ; and, if the restiform tracts of the medulla
oblongata be irritated, the most acute suffering appears to
be produced. Its removal or disorganization by disease is
also generally unaccompanied with loss or disorder of
sensibility ; animals from which it is removed can smell, »
see, hear, and feel pain, to all appearance, as perfectly as

Fig. 148.*

before (Flourens; Magendie). So that, although the resti-
form tracts of the medulla oblongata, which themselves |
appear so sensitive, enter the cerebellum, it cannot be re-
garded as a principal organ of sensibility.

In reference to motion, the experiments of Longet and
most others agree that no irritation of the cerebellum
produces movement of any kind. Remarkable results,

* Fig. 148. Outline sketch of a section of the cerebellum, showing
the corpus dentatum (from Quain). %.—The section has been carried
through the left lateral part of the pons, so as to divide the superior
peduncle and pass nearly through the middle of the left cerebellar hemi-
sphere. The olivary body has also been divided longitudinally so as to
expose in section its corpus dentatum. c¢7, crus cerebri ; f, fillet ; g,
corpora quadrigemina ; sp, superior peduncle of the cerebellum divided ;
mp, middle peduncle or lateral part of the pons Varolii, with fibres |
passing from it into the white stem ; av, continuation ofthe white stem
radiating towards the arbor vite of the folia ; ¢ d, corpus dentatum ; 0,
olivary body with its corpus dentatum ; py, anterior pyramid,

fg eo xo) ae Te ee

i bg

FUNCTIONS OF THE CEREBELLUM. 527

however, are produced by removing parts of its substance.
Flourens (whose experiments have been abundantly con-
firmed by those of Bouillaud, Longet, and others) extir-
pated the cerebellum in birds by successive layers. Feeble-
ness and want of harmony of the movements were the
consequence of removing the superficial layers. When he
reached the middle layers, the animals became restless
without being convulsed; their movements were violent
and irregular, but their sight and hearing were perfect.
By the time that the last portion of the organ was cut
away, the animals had entirely lost the powers of spring-
ing, flying, walking, standing, and preserving their equi-
librium. When an animal in this state was laid upon its.
back, it could not recover its former posture; but it
fluttered its wings and did not lie in a state of stupor; it
saw the blow that threatened it, and endeavoured to avoid
it. Volition, sensation, and memory, therefore, weré not
lost, but merely the faculty of combining the actions of the
muscles; and the endeavours of the animal to maintain its
balance were like those of a drunken man.

The experiments afforded the same results when repeated
on all classes of animals; and, from them and the others
before referred to, Flourens inferred that the cerebellum
belongs neither to the sensitive nor the intellectual appa-
ratus; and that it is not the source of voluntary movements,
although it belongs to the motor-apparatus; but is the
organ for the co-ordination of the voluntary movements, or
for the excitement of the combined action of muscles.

Such evidence as can be obtained from cases of disease of
this organ confirms the view taken by Flourens ; and, on
the whole, it gains support from comparative anatomy ;
animals whose natural movements require most frequent
and exact combinations of muscular actions being those
whose cerebella are most developed in proportion to the
spinal cord. —

M. Foville holds that the cerebellum is the organ of

528 THE NERVOUS SYSTEM.

muscular sense, i.e., the organ by which the mind acquires
that knowledge of the actual state and position of the
muscles which is essential to the exercise of the will upon
them; and it must be admitted that all the facts just
referred to are as well explained on this hypothesis as on
that of the cerebellum being the organ for combining
movements. A harmonious combination of muscular
actions must depend as much on the capability of appre-
ciating the condition of the muscles with regard to their
tension, and to the force with which they are contracting, —
as on the power which any special nerve-centre may possess
of exciting them to contraction. And it is because the
power of such harmonious movement would be equally
lost, whether the injury to the cerebellum involved injury
to the seat of muscular sense, or to the centre for com-
bining muscular actions, that experiments on the subject
afford no proof in one direction more than the other.

Gall was led to believe, that the cerebellum is the organ
of physical love, or, as Spurzheim called it, of amativeness;
and this view is generally received by phrenologists. The
facts favouring it are, first, several cases in which atrophy
of the testes and loss of sexual passion have been the
consequence of blows over the cerebellum, or wounds of its
substance ; secondly, cases in which disease of the cere-
bellum has been attended with almost constant erection of
the penis, and frequent seminal emissions; and thirdly,
that it has seemed possible to estimate the degree of sexual
passion in different persons by an external examination of
the region of the cerebellum.

The cases of disease of the cerebellum do not prove
much; for the same affections of the genital organs are
more generally observed in diseases, and in experimental
irritations of the medulla oblongata and upper part of the
spinal cord (Longet).

The facts drawn from craniological examination will
receive the credit given to the system of which they are a

/

FUNCTIONS OF THE CEREBELLUM. 529

principal evidence. But, in opposition to them, it must be
stated that there has been a case of complete disorganiza-
tion or absence of the cerebellum without loss of sexual —
passion (Combiette, Longet, and Cruveilhier); that the
cocks from whom M. Flourens removed the cerebellum
showed sexual desire, though they were ‘incapable of
gratifying it; and that among animals there is no pro-
portion observable between the size of the cerebellum and
the development of the sexual passion. On the con-
trary, many instances may be mentioned in which a larger
sexual appetite co-exists with a smaller cerebellum; as
é.g., that rays and eels, which are among the fish that

‘copulate, have not laminz on their almost rudimental

cerebella; and that cod-fish, which do not copulate, but
deposit their generative fluids in the water, have com-
paratively well-developed cerebella. Among the Amphibia,
the sexual passion is apparently very strong in frogs and
toads; yet the cerebellum is only a narrow bar of nervous
substance. Among birds there is no enlargement of the
cerebellum in the males that are polygamous ; the domestic
cock’s cerebellum is not larger than the hen’s, though his
sexual passion must be estimated at many times greater
than hers. Among Mammalia the same rule holds; and
in this class the experiments of M. Lassaigne have plainly
shown that the abolition of the sexual passion by removal
of the testes in early life is not followed by any diminu-
tion of the cerebellum; for in mares and stallions the
average absolute weight of the cerebellum is 61 grains,
and in geldings 70 grains; and its proportionate weight,
compared with that of the cerebrum, is, on average, as
I: 6°59 in mares; as I: 5°97 in geldings, and only as
I : 7°07 in stallions. 7

On the whole, therefore, it appears advisable te wait for
more evidence before concluding that there is any peculiar
and direct connection between the cerebellum and the

sexual instinct or sexual passion. From all that has
) MM

530 ‘THE NERVOUS SYSTEM.

been observed, no other office is manifest in it than that
of regulating and combining muscular movements, or of
enabling them to be regulated and combined by so inform-
ing the mind of the state and position of the muscles that
the will may be definitely and aptly directed to them.

The influence of each half of the cerebellum is directed
to muscles on the opposite side of the body; and it would
appear that for the right ordering ‘of movements, the
actions of its two halves must be always mutually balanced
and adjusted. For if one of its crura, or if the pons on
either side of the middle line, be divided, so as to cut off
from the medulla oblongata and spinal cord the influence
of one of the hemispheres of the cerebellum, strangely
disordered movements ensue. The animals fall down on
the side opposite to that on which the crus cerebelli has
been divided, and then roll over continuously and re- _
peatedly; the rotation being always round the long axis
of their bodies, and from the side on which the injury has
been inflicted.* “The rotations sometimes take place with
much rapidity; as often, according ‘to M. Magendie, as
sixty times in a minute, and may last for several days.
Similar movements have been observed in men; as by M.
Serres in a man in whom there was apoplectic effusion in
the right crus cerebelli; and by M. Belhomme in a woman,
in whom an exostosis pressed on the left crus.t They

4

* Magendie and Miller, and others following him, say the rotation
is towards the injured side; but Longet and others more correctly give
the statement as in the text. The difference has probably arisen from
using the words right and left, without saying whose right and left are
meant, whether those of the observer or those of the observed. When,
for example, an animal’s right crus cerebelli is divided, he rolls from his
own right to his own left, but from the left to the right of one who is
standing in front of him.

t See such cases collected and recorded by Dr. Pagetin the Ed. Med.
and Surg. Journal for 1847.

FUNCTIONS OF THE CEREBRUM. 531

may, perhaps, be explained by assuming that the division
or injury of the crus cerebelli produces paralysis or
imperfect and disorderly movements of the opposite side
of the body; the animal falls, and then, struggling with
the disordered side on the ground, and striving to rise with
the other, pushes itself over; and so, again and again,
with the same act, rotates itself. Such movements cease ~

“when the other crus cerebelli is divided; but probably only

because the paralysis of the body is thus made almost
complete.

‘STRUCTURE AND PHYSIOLOGY OF THE CEREBRUM.

The cerebrum is placed in connection with the pons and
medulla oblongata by its two crura or peduneles (fig. 149) :
it is connected with the cerebellum, by the processes called
superior crura of the cerebellum, or processus a cerebello ad
testes, and by a layer of grey matter, called the valve of
Vieussens, which lies between these processes, and extends
from the inferior vermiform process of the cerebellum to
the corpora quadrigemina of the cerebrum. These parts,
which thus connect the cerebrum with the other princi-
pal divisions of the cerebro-spinal nervous centre, form
parts of the walls of a cavity (the fourth ventricle) and a
canal (the iter a tertio ad quartum ventriculum) which are
the continuation of the canal that in the foetus extended
through the whole length of the spinal cord and brain.
They may, therefore, be regarded as the continuation of
the cerebro-spinal axis or column; on which, as a develop-
ment from the simple type, the cerebellum is placed; and,
on the further continuation of which, structures both larger
and more numerous are raised, to form the cerebrum
(fig. 142).

The cerebral convolutions appear to be formed of nearly
parallel plates of fibres, the ends of which are turned

towards the surface of the brain, and are overlaid and
M M 2

'

a

ee THE NERVOUS SYSTEM.

mingled with successive layers of grey nerve-substance. |
The external grey matter is so arranged in layers, that a
vertical section of a convolution, according to Mr. Lockhart

Fig. 149.*

Clarke, generally presents the appearance of seven layers
of pale and dark nervous substance. The structure of the
grey matter is that which belongs to vesicular nervous
substance (p. 473).

It is nearly certain that the cerebral hemispheres are
the organs by which,—ist, we perceive those clear and
more impressive sensations which we can retain, and

* Fig. 149. Plan in outline of the encephalon, as seen from the right
side. 4. (From Quain).—The parts are represented as separated from
one another somewhat more than natural, so as to show their connec-
tions. A, cerebrum ;/f, g, h, its anterior, middle, and posterior lobes ;

é, fissure of Sylvius; B, cerebellum; C, pons Varolii; D, medulla —

oblongata ; a, peduncles of the cerebrum ; 0, c, d, superior, middle,
and inferior peduncles of the cerebellum.

:
|

FUNCTIONS OF THE CEREBRUM. 533

according to which we can judge; 2ndly, by which are
performed those acts of will, each of which requires a
deliberate, however quick, determination; 3rdly, they are
the means of retaining impressions of sensible things, and

_ reproducing them in subjective sensations and ideas;

Athly, they are the medium of the higher emotions and

feelings, and of the faculties of judgment, understanding,

memory, reflection, induction, and imagination, and others
of a like class.

The evidences that the cerebral hemispheres have the
functions indicated above, are chiefly these:—1r. That any
severe injury of them, such as a general concussion, or
sudden pressure by apoplexy, may instantly deprive a
man of all power of manifesting externally any mental
faculty. 2. That in the same general proportion as the
higher sensuous mental faculties are developed in the
vertebrate animals, and in man at different ages, the more
is the size of the cerebral hemispheres developed in com-
parison with the rest of the cerebro-spinal system. 3. That
no other part of the nervous system bears a corresponding
proportion to the development of the mental faculties.
4. That congenital and other morbid defects of the cerebral .
hemispheres are, in general, accompanied with correspond-
ing deficiency in the range or power of the intellectual
faculties and the higher instincts.

Respecting the mode in which the brain discharges its
functions, there is no evidence whatever. But it appears
that, for all but its highest intellectual acts, one of the
cerebral hemispheres is sufficient. For numerous cases
are recorded in which no mental defect was observed,
although one cerebral hemisphere was so disorganised or
atrophied that it could not be supposed capable of dis-
charging its functions. The remaining hemisphere was,
in these cases, adequate to the functions generally dis-
charged by both; but the mind does not seem in any of
these cases to have been tested. in very high intellectual

554 THE NERVOUS SYSTEM.

.

exercises; so that it is not certain that one hemisphere
will suffice for these. In general, the mind combines, as
one sensation, the impressions which it derives from one
object through both hemispheres, and the ideas to which
the two such impressions give rise are single.

In relation to common sensation and the effort of the
will, the impressions to and from the hemispheres of the
brain are carried across the middle line; so that in destruc-
tion or compression of either hemisphere, whatever effects
are produced in loss of sensation or voluntary motion, are
observed on the side of the > body Y opposite to that on which
the brain is injured.
ie Sn speaking of the cerebral hemispheres as the so-called

organs of the mind, they have been regarded as if they
were single organs, of which all parts are equally appro-
priate for the exercise of each of the mental faculties. But
it is possible that each faculty has a special portion of the
brain appropriated to it as its proper organ. For this theory
the principal evidences are as follows:—1. That it is in
accordance with the physiology of the other compound
organs or systems in the body, in which each part has its
special function; as, for example, of the digestive system,
in which the stomach, liver, and other organs perform each
their separate share in the general process of the digestion
of the food. 2. That in different individuals the several
mental functions are manifested in very different degrees.
Even in early childhood, before education can be imagined
to have exercised any influence on the mind, children
exhibit various dispositions—each presents some predomi-
nant propensity, or evinces a singular aptness in some
study or pursuit; and it is a matter of daily observation -
that every one has his peculiar talent or propensity. But
it is difficult to imagine how this could be the case, if the
manifestation of each faculty depended on the whole of the
brain: different conditions of the whole mass might affect
the mind generally, depressing or exalting all its functions

FUNCTIONS OF THE CEREBRUM. 535

in an equal degree, but could not permit one faculty to
be strongly and another weakly manifested. 3. The
plurality of organs in the brain is supported by the phe-
nomena of some forms of mental derangement. It is not
usual for all the mental faculties in an insane person to be
equally disordered ; it often happens that the strength of
some is increased, while that of others is diminished; and
in many cases one function only of the mind is deranged,
while all the rest are performed in a natural manner. 4.
The same opinion is supported by the fact that the several
mental faculties are developed to their greatest strength at
different periods of life, some being exercised with great
energy in childhood, others only in adult age; and that
as their energy decreases in old age, there is not a gradual
and equal diminution of power in all of them at once, but,
on the contrary, a diminution in oneor more, while others
retain their full strength, or even increase in power. 5.
The plurality of cerebral organs appears to be indicated
by the phenomena of dreams, in which only a part of the
mental faculties are at rest or asleep, while the others
are awake, and, it is presumed, are exercised through
the medium’ of the parts of the brain appropriated to
them.

These facts have been so illustrated and adapted by
phrenologists, that the theory of the plurality of organs
in the cerebrum, thus made probable, has been commonly
regarded as peculiar to phrenology, and as so essentially
connected with it, that if the system of Gall and Spurzheim
be untrue, this theory cannot be maintained. But it is
plain that all the system of phrenology built upon the
theory may be false, and the theory itself true; for phre-
nologists assume, not only this theory, but also that they
have determined all the primitive faculties, of which the
mind consists, i.e., all the faculties to which special
organs must be assigned, and the places of all those
organs in the cerebral hemispheres and the cerebellum,

530 : THE NERVOUS SYSTEM. »

That this is a system of error there need be no doubt,
but it is possibly founded on a true theory: the cere-
brum may have many organs, and the mind as many
faculties ; but what are the faculties that require separate
organs, and where those organs are situate, are subjects
of which only the most general and rudimentary know-
ledge has been yet attained.

From the apparently greater frequency of interference
with the faculty of speech in disease of the left than of the
right half of the cerebrum, it has been thought that the
nerve-centre for language, including in this term all intel-

| lectual expression of ideas, is situate in the left cerebral
hemisphere. It cannot be said, however, that the ‘existing
evidence for this theory is at present sufficient to have
\ established it.

Of the physiology of the other parts of the brain, little
or nothing can be said.

Of the offices of the corpus callosum, or great transverse
and oblique commissure of the brain, nothing positive is
known. But instances in which it was absent, or very
deficient, either without any evident mental defect, or with
only such as might be ascribed to coincident affections of
other parts, make it probable that the office which is com-
monly assigned to it, of enabling the two sides of the brain
to act in concord, is exercised only in the highest acts of
which the mind is capable. And this view is confirmed
by the very late period of its development, and by its
absence in all but the placental Mammalia.*

To the fornix and other commissures no special function
can be assigned; but it is a reasonable hypothesis that
they connect the action of the parts between which they
are severally placed.

* See cases of congenital deficiency of the corpus callosum, by Mr.
Paget and Mr. Henry, in the twenty-ninth and thirty-first volumes of
the Medico-Chirurgical Transactions.

pe
’

ee

oe ay aren

on eee

THE CORPUS CALLOSUM. 537

As little is known ot the function of the pineal and

Fig. 150.*

* Fig. 150. View of the corpus callosum from above (from Sappey
after Foville). 4.—The upper surface of the corpus callosum has been
fully exposed by separating the cerebral hemispheres and throwing them
to the side ; the gyrus fornicatus has been detached, and the transverse
fibres of the corpus callosum traced for some distance into the cerebral
medullary substance. 1, the upper surface of the corpus callosum ; 2,
median furrow or raphe ; 3, longitudinal strie bounding the furrow ;
4, swelling formed by the transverse bands as they pass into the cere-
brum ; 5, anterior extremity or knee of the corpus callosum ; 6, posterior
extremity ; 7, anterior, and 8, posterior part of the mass of fibres pro-
ceeding from the corpus callosum ; 9, margin of the swelling ; 10, ante-
rior part of the convolution of the corpus callosum ; 11, hem or band
of union of this convolution ; 12, internal convolutions of the parietal
lobe ; 13, upper surface of the cerebellum.

538 THE NERVOUS SYSTEM:

pituitary glands. The latter has been supposed, from its
microscopic structure, to be rather a ductless gland (p. 410)
than a nervous organ.

PHYSIOLOGY OF THE CEREBRAL AND SPINAL NERVES.

The cerebral nerves are commonly enumerated as nine
pairs, but the number is in reality twelve, the seventh nerve
consisting, as it does, of two nerves, and the eighth of three.
These and the spinal nerves, of which there are thirty-one
pairs, symmetrically arranged on each side of what, re-

duced to its simplest form, may be regarded as a column
or axis of nervous matter, extending from the olfactory
bulbs on the ethmoid bone to the filum- terminale of the
spinal cord in the lumbar and sacral portions of the ver-
tebral canal. The spinal nerves all present certain cha-—
racters in common, such as their double roots; the isolation
of the fibres of sensation in the posterior roots, and those
of motion in the anterior roots; the formation of the gan-
glia on the posterior root; and the subsequent mingling
of the fibres in trunks and branches of mixed functions.
Similar characters probably belong essentially to the cere-
bral nerves; but even when one includes the nerves of
special sense, it is not possible to discern a conformity of
arrangement in any besides the fifth, or trifacial, which,
from its many analogies to the spinal nerves, Sir Charles
Bell designed as a spinal nerve of the head.

According to their several functions, the cerebral or
cranial nerves may be thus arranged :—

Nerves of special sense . Olfactory, optic, auditory, part of the glosso-
pharyngeal, and the lingual branch of the
fifth.

», of common sensation. The greater portion of the fifth, and part of
the glosso-pharyngeal.,

THE CEREBRAL NERVES. 539

{
Nerves of motion . . Third, fourth, lesser division of the fifth,

sixth, facial, and hypoglossal.
Mixed nerves. . . . Pneumogastric, and accessory.

The physiology of the seyeral nerves of the special senses
will be considered with the organs of those senses.

Physiology of the Third, Fourth, and Sixth Cerebral or
Cranial Nerves.

The physiology of these nerves may be in some degree
combined, because of their intimate connection with each
other in the actions of the muscles of the eyeball, which
they supply. They are probably all formed exclusively of
motor fibres: some pain is indicated when the trunk of the
third nerve is irritated near its origin; but this may be
-because of some filaments of the fifth nerve running back-
wards to the brain in the trunk of the third, or because
adjacent sensitive parts are involved in the irritation.

The third nerve, or motor oculi, supplies the levator
palpebree superioris muscle, and, of the muscles of the eye-
ball, all but.tne superior oblique or trochlearis, to which
the fourth nerve is appropriated, and the rectus externus
which receives the sixth nerve. Through the medium of
the ophthalmic or lenticular ganglion, of which it forms
what is called the short root, it also supplies the motor
filaments to the iris. one
~ When the third nerve is irritated within the skull, all
those muscles to which it is distributed are convulsed.
When it is paralysed or divided, the following effects
ensue : first, the upper eyelid can be no longer raised by
the levator palpebrze, but drops and remains gently closed
over the eye, under the unbalanced influence of the orbi-
cularis palpebrarum, which is supplied by the facial nerve:
secondly, the eye is turned outwards by the unbalanced
action of the rectus externus, to which the sixth nerve is
appropriated : and hence, from the irregularity of the axes |

540 THE NERVOUS SYSTEM,

of the eyes, double-sight is often experienced when a single
object is within view of both the eyes: thirdly, the eye
cannot be moved either upwards, downwards, or inwards;
fourthly, the pupil is dilated.

The relation of the third nerve to the iris is of peculiar
interest. In ordinary circumstances the contraction of the
iris is a reflex action, which may be explained as produced
by the stimulus of light on the retina being conveyed by
the optic nerve to the brain (probably to the corpora
quadrigemina), and thence reflected through the third
nerve to the iris. Hence the iris ceases to act when either
the optic or the third nerve is divided or destroyed, or
when the’ corpora quadrigemina are destroyed or much
compressed. But when the optic nerve is divided, the
contraction of the iris may be excited by irritating that
portion of the nerve which is connected with the brain;
aud when the third nerve is divided, the irritation of its
distal portion will still excite contraction of the iris in
which its fibres are distributed.

The contraction of the iris thus shows all the character
of a reflex act, and in ordinary cases requires the concurrent
action of the optic nerve, corpora quadrigemina, and third
nerve ; and, probably also, considering the peculiarities of
its perfect mode of action, the ophthalmic ganglion. But,
besides, both irides will contract their pupils under the
reflected stimulus of light falling only on one retina or
under irritation of one optic nerve. Thus, in amaurosis of
one eye, its pupil may contract when the other eye is ex-
posed to a stronger light: and generally the contraction of
each of the pupils appears to be in direct proportion to the
total quantity of light which stimulates either one or both
retinze, according as one or both eyes are open.

The iris acts also in association with certain other
muscles supplied by the third nerve: thus, when the eye —
is directed inwards, or upwards and inwards, by the action
of the third nerve distributed in the rectus internus and

PAS

te ee

THE CEREBRAL NERVES. 541

rectus superior, the iris contracts, as if under direct volun-

tary influence. The will cannot, however, act on the iris

alone through the third nerve; but this aptness to contract
in association with the other muscles supplied by the third,
may be sufficient to make it act even in total blindness and
insensibility of the retina, whenever these muscles are
contracted. The contraction of the pupils, when the eyes

are moved inwards, as in looking at a near object, has |

probably the purpose of excluding those outermost rays of
light which would be too far divergent to be refracted to
a clear image on the retina; and the dilatation in looking
straight forwards, as in looking at a distant object, permits
the admission of the largest number of rays, of which none
are too divergent to be so refracted.

The fourth nerve, or Nervus trochlearis, or patheticus, is
exclusively motor, and supplies only the trochlearis or

obliquus superior muscle of the eyeball.

The sixth nerve, Nervus abducens or ocularis externus, is
also, like the fourth, exclusively motor, and supplies only
the rectus externus muscle.* The rectus externus is,
therefore convulsed, and the eye is turned outwards, when
the sixth nerve is irritated; and the muscle paralyzed
when the nerve is disorganized, compressed, or divided.
In all such cases of paralysis, the eye squints inwards,
and cannot be moved outwards.

In its course through the cavernous sinus, the sixth
nerve forms larger communications with the sympathetic
nerve than any other nerve within the cavity of the skull
does. But the import of these communications with the

sympathetic, and the subsequent distribution of its fila-

* In several animals it sends filaments to the iris (Radclyfie Hall) ;
and it has probably done so in man, in some instances in which the iris
has not been paralyzed, while all the other parts supplied by the third
nerve were (Grant).

'

I Se

542 THE NERVOUS SYSTEM.

ments after joining the sixth nerve, are quite unknown ;
and there is no reason to believe that the sixth nerve is, in
function, more closely connected with the sympathetic than
any other cerebral nerve is.

The question has often suggested itself why the six
muscles of the eyeball should be supplied by three motor
merves when all of them are within reach of the branches
of one nerve; and the true explanation would have more
interest than attaches to the movements of the eye alone;
since it is probable that we have, in this instance, within
a small space, an example of some general rule according
to which associate or antagonist muscles are supplied with ~
motor nerves.

Now, in the several movements of the eyes, we sometimes
have to act with symmetrically-placed muscles, as when
both eyes are turned upwards or downwards, inwards or
outwards.* All the symmetrically-placed muscles are sup-
plied with symmetrical nerves, i.e., with corresponding
branches of the same nerves on the two sides; and the
action of these symmetrical muscles is easy and natural,
as we have a natural tendency to symmetrical movement
in most parts. But because of this tendency to symme-
trical movements of muscles supplied by symmetrical
nerves, it would appear as if, when the two eyes are to be
moved otherwise than symmetrically, the muscles to effect
such a movement must be supplied with different nerves.
So, when the two eyes are to be turned towards one side,
say the right, by the action of the rectus externus of the
right eye and the rectus internus of the left, it appears as
if the tendency to action through the similar branches of
corresponding nerves (which would move both eyes in-
wards or outwards) were corrected by one of these muscles

* It is sometimes said, that the external recti cannot be put /in
action simultaneously : yet they are so when the eyes, having been —
both directed inwards, are restored to the position which they have in
looking straight forwards.

THE FIFTH TERMINAL NERVE. 543

being supplied by the sixth, and the other by the third
nerve. So with the oblique muscles: the simplest and
easiest actions would be through branches of the corre-
sponding nerves, acting similarly as symmetrical muscles ;
but the necessary movements of the two eyes require the
contraction of the superior oblique of one side, to be asso-
ciated with the contraction of the inferior oblique and the
relaxation of the superior oblique, of the opposite side-
For this, the fourth nerve of one side is made to act with
a branch of the third nerve of the other; as if thus the
tendency to simultaneous action through the similar nerves
of the two sides were prevented. At any rate, the rule of
distribution of nerves here seems to be, that when in
frequent and necessary movements any muscle has to act
with the antagonist of its fellow on the opposite side, it
and its fellow’s antagonist are supplied from different
nerves.

Physiology of the Fifth or Trigeminal Nerve.

The fifth or trigeminal nerve resembles, as already
stated, the spiual nerves, in that its branches are derived
through two roots; namely, the larger or sensitive, in
connection with which is the Gasserian ganglion, and the
smaller or motor root which has no ganglion, and which
passes under the ganglion ,of the sensitive root to join the
¢hird branch or division which issues from it. The first
and second divisions of the nerve, which arise wholly from
the larger root, are purely sensitive. The third division
being joined, as before said, by the motor root of the nerve,
is of course both motor and sensitive.

Through the branches of the greater or ganglionic por-
tion of the fifth nerve, all the anterior and antero-lateral
parts of the face and head, with the exception of the skin
of the parotid region (which derives branches from the
cervical spinal nerves), acquire common 'sénsibility ; and
among these parts may be included the organs of special

B44 THE NERVOUS SYSTEM.

sense, from which common sensations are conveyed through
the fifth nerve, and their peculiar sensation through their
several nerves of special sense. The muscles, also, of the
face and lower jaw acquire muscular sensibility through
the filaments of the ganglionic portion of the fifth nerve
distributed to them with their proper motor nerves.
Through branches of the lesser or non-ganglionic por-
tion of the fifth, the muscles of mastication, namely, the
temporal, masseter, two pterygoid, anterior part of the
digastric, and mylo-hyoid, derive their motor nerves. The
motor function of these branches is proved by the violent

contraction of all the muscles of mastication in experi- °

mental irritation of the third, or inferior maxillary, divi-
sion of the nerve ; by paralysis of the same muscles, when it
is divided or disorganized, or from any reason deprived of
power ; and by the retention of the power of these muscles,
when all those supplied by the facial nerve lose their power

through paralysis of that nerve. The last instance proves .

best, that though the buccinator muscle gives passage to,
and receives some filaments from, a buccal branch of the
inferior division of the fifth nerve, yet it derives its motor
power from the facial, for it is paralyzed together with the
other muscles that are supplied by the facial, but retains
its power when the other muscles of mastication are
paralyzed. Whether, however, the branch of the fifth
nerve which is supplied to the buccinator muscle is entirely
sensitive, or in part motor also, must remain for the present
doubtful. From the fact that this muscle, besides its other
functions, acts in concert or harmony with the muscles of
mastication, in keeping the food between the teeth, it might
be supposed from analogy, that it would have a motor
branch from the same nerve that supplies them. There
can be no doubt, however, that the so-called buccal branch
of the fifth, is, in the main, sensitive; although it is not

quite certain that it may not give a few motor filaments to

the buccinator muscle.

>

ae So ee ee

Sah is Adeah leat sthatieaeiaed
hiee?

Sor eo

THE FIFTH CEREBRAL NERVE. 545

The sensitive function of the branches of the greater
division of the fifth nerve is proved by all the usual evi-
dences, such as their distribution in parts that are sensitive
and not capable of muscular contraction, the exceeding
sensibility of some of these parts, their loss of sensation
when the nerve is paralyzed or divided, the pain without
convulsions produced by morbid or experimental irritation
of the trunk or branches of the nerve, and the analogy of
this portion of the fifth to the posterior root of the spinal
nerve.

_ But although formed of sensitive filaments exclusively,
the branches of the greater or ganglionic portion of the
fifth nerve exercise a manifold influence on the movements
of the muscles of the head and face, and other parts in
which they are distributed. They do so, in the first place,
by providing the muscles themselves with that sensibility
without which the mind, being unconscious of their position
and state, cannot voluntarily exercise them. It is, pro-
bably, for conferring this sensibility on the muscles, that
the branches of the fifth nerve communicate so frequently
with those of tae facial and hypoglossal, and the nerves of
the muscles of the eye; and it is because of the loss of this
sensibility that when the fifth nerve is divided, animals are
always slow and awkward in the movement of the muscles
of the face and head, or hold them still, or guide their
movements by the sight of the objects towards which they
wish to move.

Again, the fifth nerve has an indirect influence on the

- muscular movements, by conveying sensations of the state

and position of the skin and other parts: which the mind
perceiving, is enabled to determine appropriate acts. Thus,
when the fifth nerve or its infra-orbital branch is divided,
the movements of [the lips in feeding may cease, or be im-
perfect ; a fact which led Sir Charles Bell into one of the
very few errors of his physiology of the nerves. He sup-
posed that the motion of the upper lip, in grasping food,
NN

546 | THE NERVOUS SYSTEM.

depended directly on the infra-orbital nerve; for he found
that, after he had divided that nerve on both sides in an
ass, it no longer seized the food with its lips, but merely
pressed them against the ground, and used the tongue for
the prehension of the food. Mr. Mayo corrected this error.
He found, indeed, that after the infra-orbital nerve had
been divided, the animal did not seize its food with the lip,
and could not use it well during mastication, but that it
could open the lips. He, therefore, justly attributed the
phenomena in Sir C. Bell’s experiments to the loss of
sensation in the lips; the animal not being able to feel the
food, and, therefore, although it had the power to seize it,
not knowing how or where to use that power.

Lastly, the fifth nerve has an intimate connection with
muscular movements through the many reflex acts of
muscles of which it is the necessary excitant. Hence, when
it is divided, and can no longer convey impressions to the
nervous centres to be thence reflected, the irritation of the
conjunctiva produces no closure of the eye, the mechanical
irritation of the nose excites no sneezing, that of the tongue
no flowing of saliva; and although tears and saliva may
flow naturally, their afflux is not increased by the me-
chanical or chemical or other stimuli, to the indirect or
reflected influence of which it is liable in the perfect state
of this nerve.

The fifth nerve, though its ciliary branches and the
branch which forms the long root of the ciliary or ophthal-
mic ganglion, exercises also some influence on the move-
ments of the iris. When the trunk of the ophthalmic
portion is divided, the pupil becomes, according to Valentin,
contracted in men and rabbits, and dilated in cats and
dogs; but in all cases, becomes immovable, even under all
the varieties of the stimulus of light. How the fifth nerve
thus affects the iris is unexplained; the same effects are
produced by destruction of the superior cervical ganglion
of the sympathetic, so that, possibly, they are due to the

THE FIFTH CEREBRAL NERVE. 547
injury of those filaments of the sympathetic which, after
joining the trunk of the fifth, at and beyond the Gasserian
- ganglion, proceed with the branches of its ophthalmic divi-
sion to the iris; or, as Dr. R. Hall ingeniously suggests,
the influence of the fifth nerve on the movements of the
iris may be ascribed to the affection of vision in consequence
of the disturbed circulation or nutrition in the retina, when
the normal influence of the fifth nerve and ciliary ganglion
is disturbed. In such disturbance, increased circulation
making the retina more irritable might induce extreme
contraction of the iris; or, under moderate stimulus of
light, producing partial blindness, might induce dilatation:
but it does not appear why, if this be the true explanation,
the iris should in either case be immovable and unaffected
by the various degrees of light.

Furthermore, the morbid effects which division of the
fifth nerve produces in the organs of special sense, make
it probable that, in the normal state, the fifth nerve exer-
cises some indirect influence on all these organs or their
functions. Thus, after such division, within a period
varying frori twenty-four hours to a week, the cornea
begins to be opaque; then it grows completely white; a
low destructive inflammatory process ensues in the con-
junctiva, sclerotica, and interior parts of the eye; and
within one or a few weeks, the whole eye may be quite
disorganized, and the cornea may slough or be pene-
trated by a large ulcer. The sense of smell (and not
merely that of mechanical irritation of the nose), may be
at the same time lost, or gravely impaired; so may the
hearing, and commonly, whenever the fifth nerve is para-
lyzed, the tongue loses the sense of taste in its anterior and
lateral parts, i.¢., in the portion in which the lingual or
gustatory branch of the inferior maxillary division of the
fifth is distributed.*

* That complete paralysis of the fifth nerve may, however, be unac-

companied, at least, for a considerable period, by injury to the organs
; NN 2

548 THE NERVOUS SYSTEM.

' The loss of the sense of taste is no doubt chiefly due to
the lingual branch of the fifth nerve being a nerve of
special sense; partly, also, perhaps, it is due to the fact
that this branch supplies, in the anterior and lateral
parts of the tongue, a necessary condition for the proper
nutrition of that part. But, deferring this question until
the glosso-pharyngeal nerve is to be considered, it may be
observed that in some brief time after complete paralysis
or division of the fifth nerve, the power of all the organs
of the special senses may be lost; they may lose not
merely their sensibility to common impressions, for which
they all depend directly on the fifth nerve, but also their
sensibility to the several peculiar impressions for the
reception and conduction of which they are purposely
constructed and supplied with special nerves besides the
fifth. The facts observed in these cases* can, perhaps, be
only explained by the influence which the fifth nerve
exercises on the nutritive processes in the organs of the
special senses. It is not unreasonable to believe, that, in
paralysis of the fifth nerve, their tissues may be the seats
of such changes as are seen in the laxity, the vascular
congestion, osdema, and other affections of the skin of the
face and other tegumentary parts which also accompany
the paralysis; and that these changes, which may appear
unimportant when they aflect external parts, are suffi-
cient to destroy that refinement of structure by which
the organs of the special senses are adapted to their
functions.

According to Magendie and Longet, destruction of the
eye ensues more quickly after division of the trunk of
the fifth beyond the Gasserian ganglion, or after divi-

of special sense, with the exception of that portion of the tongue which
is supplied by its gustatory branch, is well illustrated by a valuable
case lately recorded by Dr. Althaus.

* Two of the best cases are published, with analyses of others, by
Mr. Dixon, in the Medico-Chirurgical Transactions, vol. xxviii.

THE FIFTH CEREBRAL NERVE. 549

sion of the ophthalmic branch, than after division of the

roots of the fifth between the brain and the ganglion.

Hence it would appear as if the influence on nutrition
were conveyed through the filaments of the sympathetic,
which join the branches of the fifth nerve at and beyond
the Gasserian ganglion, rather than through the filaments
of the fifth itself; and this is confirmed by experiments
in which extirpation of the superior cervical ganglion of
the sympathetic produced the same destructive disease
of the eye that commonly follows the division of the fifth
nerve.

And yet, that the filaments of the fifth nerve, as well as
those of the sympathetic, may conduct such influence, ap-
pears certain from the cases, including that by Mr. Stanley,
in which the source of the paralysis of the fifth nerve was
near the brain, or at its very origin, before it receives any °

- communication from the sympathetic nerve. The existence

of ganglia of the sympathetic in connection with all the
principal divisions of the fifth nerve where it gives off
those branches which supply the organs of special sense
—for example, the connection of the ophthalmic ganglion
with the ophthalmic nerve at the origin of the ciliary
nerves ; of the spheno-palatine ganglion with the superior
maxillary division, where it gives its branches to the nose
and the palate; of the otic ganglion with the inferior
maxillary near the giving off of filaments to the internal
ear; and of the sub-maxillary ganglion with the lingual
branch of the fifth—all these connections suggest that a
peculiar and probably conjoint influence of the sympa-
thetic and fifth nerves is exercised in the nutrition of the
organs of the special senses; and the results of experi-
ment and disease confirm this, by showing that the nutri-
tion of the organs may be impaired in consequence of im-
pairment of the power of either of the nerves.

A possible connection between the fifth nerve and the
sense of sight, is shown in cases of no unfrequent occur-

550 THE NERVOUS SYSTEM.

rence, in which blows or other injuries implicating the
frontal nerve as it passes over the brow, are followed by
total blindness in the corresponding eye. The blindness
appears to be the consequence of defective nutrition of the
retina; for although, in some cases, it has ensued imme-
diately, as if from concussion of the retina, yet in some
it has come on gradually like slowly progressive amau-
rosis, and in some with inflammatory disorganisation,
followed by atrophy of the whole eye.*

Physiology of the Facial Nerve.

The facial, or portio dura of the seventh pair of nerves,
is the motor nerve of all the muscles of the face, including
the platysma, but not including any of the muscles of mas-
tication already enumerated (p. 544); it supplies, also,
the parotid gland, and through the connection of its trunk
with the Vidian nerve, by the petrosal nerves, some of the
muscles of the soft palate, most probably the levator palati
and azygos uvulz; by its tympanic branches it supplies
the stapedius and laxator tympani, and, through the otic
ganglion, the tensor tympani; through the chorda tympani
it sends branches to the submaxillary gland and to the
lingualis and some other muscular fibres of the tongue ;
and by branches given off before it comes upon the face, it
supplies the muscles of the external ear, the posterior part
of the digastricus, and the stylo-hyoideus.

To the greater number of the muscles to which it is dis--

tributed it is the sole motor nerve. No pain is produced by
irritating it near its origin (Valentin), and the indications
of pain which are elicited when any of its branches are
irritated, may be explained by the abundant communica-
tions which, in all parts of its course, it forms with sensi-

* Such a case is recorded by Snabilie inthe Nederlandsch Lancet,
August, 1846.

Mi Si -9\04 empamae

Ws aes

THE FACIAL NERVE. 551

tive nerves, whose filaments being mingled with its own
are the true source of the pain.

Besides its motor influence, the facial is also, by means
of the fibres which are supplied to the submaxillary
and parotid glands, a so-called secretory nerve (p. 475).
For through the last-named branches impressions may
be conveyed which excite increased secretion of saliva.
For example, if, in adog, the submaxillary gland be
exposed, and the chorda tympani be divided, it will
be seen that on stimulating the distal end of the
nerve by a weak electric current, the gland becomes ex-
ceedingly vascular, and saliva is secreted in largely in-
creased amount. Under ordinary circumstances of in-
creased secretion of saliva by the submaxillary gland, as
from the presence of food in the mouth, the stimulus
is conveyed by the same channel, the chorda tympani
being the efferent nerve in a reflex action, in which the

_ afferent fibres are branches of the fifth and glosso-pharyn-

geal nerves.

When the facial nerve is divided, or in any other way
paralyzed, tae loss of power in the muscles which it sup-
plies, while proving the nature and extent of its functions,
displays also the necessity of its perfection for the perfect
exercise of all the organs of the special senses. ‘Thus, in
paralysis of the facial nerve, the orbicularis palpebrarum
being powerless, the eye remains open through the un-
balanced action of the levator palpebree ; and the conjunc-
tiva, thus continually exposed to the air and the contact of
dust, is liable to repeated inflammation, which may end in
thickening and opacity of both its own tissue and that of
the cornea. These changes, however, ensue much more
slowly than those which follow paralysis of the fifth nerve,
and never bear the same destructive character. In paraly-
sis of the facial nerve, also, tears are apt to flow constantly
over the face, apparently because of the paralysis of the
tensor tarsi muscle, and the loss of the proper direction

552 THE NERVOUS SYSTEM.

and form of the orifices of the puncta lachrymalia. From
these circumstances, the sense of sight is impaired.

The sense of hearing, also, is impaired in many cases
of paralysis of the facial nerve; not only in such as are
instances of simultaneous disease in the auditory nerves,
but in such as may be explained by the loss of power in
the muscles ofthe internal ear, The sense of smell is
commonly at the same time impaired through the inability
to draw air briskly towards the upper part of the nasal
cavities, in which part alone the olfactory nerve is distri-
buted ; because, to draw the air perfectly in this direction,
the action of the dilators and compressors of the nostrils
should be perfect.

Lastly, the sense of taste is impaired, or may be wholly
lost, in paralysis of the facial nerve, provided the source
of the paralysis be in some part of the nerve between its
origin and the giving off of the chorda tympani. This
result, which has been observed in many instances of
disease of the facial nerve in man, appears explicable only
by the influence which, through the chorda tympani, it
exercises on the movements of the lingualis and the
adjacent muscular fibres of the tongue; and, according to
some, or probably in some animals, on the movements of
the stylo-glossus. We may therefore suppose that the
accurate movement of these muscles in the tongue is in
some way connected with the proper exercise of taste.

Together with these effects of paralysis of the facial
nerve, the muscles of the face being all powerless, the
countenance acquires on the paralyzed side a characteristic,
vacant look, from the absence of all expression: the angle
of the mouth is lower, and the paralyzed half of the mouth
looks longer than that on the other side; the eye has an
unmeaning stare. All these peculiarities increase, the
longer the paralysis lasts; and their appearance is exag-
gerated when at any time the muscles of the opposite side
of the face are made active in any expression, or in any of

Pes

Saige

é

Pra PRESS =

i oe al

THE GLOSSO-PHARYNGEAL NERVE. 553
their ordinary functions. In an attempt to blow or whistle,
one side of the mouth and cheek acts properly, but the
other side is motionless, or flaps loosely at the impulse of
the expired air; so in trying to suck, one side only of the
mouth acts; in feeding, the lips and cheek are powerless,
and food lodges between the cheek and gum.

As a nerve of expression, the seventh nerve must not
be considered independent of the fifth nerve, with which it
forms so many communications; for, although it is through
the facial nerve alone that all the muscles of the face are
put into their naturally expressive actions, yet the power
which the mind has of suppressing or controlling all these
expressions can only be exercised by voluntary and well-
educated actions directed through the facial nerve with the
guidance of the knowledge of the state and position of
every muscle, and this knowledge is acquired only through
the fifth nerve, which confers sensibility on the muscles,
and appears, for this purpose, to be more abundantly sup-
plied to the muscles of the face than any other sensitive
nerve is to those of other parts. .

Physiology of the Glosso-Pharyngeal Nerve.

“ The glosso-pharyngeal nerves (16, fig. 15 1), in the enume-
ration of the cerebral nerves by numbers according to the
position in which they leave the cranium, are considered as
divisions of the eighth pair of nerves, in which term are in-
cluded with them the pneumogastric and accessory nerves.
But the union of the nerves under one term is inconvenient,
although in some parts the glosso-pharyngeal and pneumo-
gastric are so combined in their distribution that it is
impossible to separate them in either anatomy or phy-
siology.

The glosso-pharyngeal nerve appears to give filaments

_ through its tympanic branch (Jacobson’s nerve), to the

fenestra ovalis, and fenestra rotunda, and the Eustachian

BoA THE NERVOUS SYSTEM.

tube ; also, to the carotid plexus, and, through the petrosal
nerve, to the spheno-palatine ganglion. After communi-
cating, either within or without the cranium, with the
pneumogastric, and soon after it leaves the cranium, with
the sympathetic, digastric branch of the facial, and the
accessory nerve, the glosso-pharyngeal nerve parts into the
two principal divisions indicated by its name, and supplies
the mucous membrane of the posterior and lateral walls of
the upper »part of the pharynx, the Eustachian tube, the
arches of the palate, the tonsils and their mucous mem-
brane, and the tongue as far forwards as the foramen
ceecum in the middle line, and to near the tip at the sides
and inferior part.

Some experiments make it probable that the glosso-
pharyngeal nerve contains, even at its origin, some motor
fibres, together with those of common sensation and the
sense of taste. Whatever motor influence, however, is
conveyed directly through the branches of the glosso-
pharyngeal, may be ascribed to the filaments of the pneu-
mogastric or accessory that are mingled with it.

The experiments of Dr. John Reid, confirming those of
Panizza and Longet, tend to the same conclusions; and
their results probably express nearly all the truth regard-
ing the part of the glosso-pharyngeal nerve which is
distributed to the pharynx. These results were that,—
I. Pain was produced when the nerve, particularly its
pharyngeal branch, was irritated. 2. Irritation of the
nerve before the origin of its pharyngeal, or of any of
these branches, gave rise to extensive muscular motions of
the throat and lower part of the face: but when the nerve
was divided, these motions were excited by irritating the
upper or cranial portion, while irritation of the lower end,
or that in connection with the muscles, was followed by
no movement; so that these motions must have depended
on a reflex influence transmitted to the muscles through
other nerves by the intervention of the nervous centres.

att “tied

MEAL eos Sm ok Lee a

— ay ryt

THE GLOSSO-PHARYNGEAL NERVE. 555

3. When the functions of the brain and medulla oblongata
were arrested by poisoning the animal with prussic acid,
irritation of the glosso-pharyngeal nerve, before it was
joined by any branches of the pneumogastric, gave rise to
no movements of the muscles of the pharynx or other parts
to which it was distributed; while, on irritating the
pharyngeal branch of the pneumogastric, or the glosso-
pharyngeal nerve, after it had received the communicating
branches just alluded to, vigorous movements of all the
pharyngeal muscles and of the upper part of the cesophagus
followed.

The most probable conclusion, therefore, may be that
what motor influence the glosso-pharyngeal nerve may
seem to exercise, is due either to the filaments of the
pneumogastric or accessory that are mingled with it, or to
impressions conveyed through it to the medulla oblongata,
and thence reflected to muscles through motor nerves,

especially the pneumogastric, accessory, and facial. Thus,

the glosso-pharyngeal nerve excites, through the medium
of the medulla oblongata, the actions of the muscles of
deglutition.. It is the chief centripetal nerve engaged in
these actions; yet not the only one, for, as Dr. John Reid
has shown, the acts are scarcely disturbed or retarded
when both the glosso-pharyngeal nerves are divided.

But besides being thus a nerve of common sensation in
the parts which it supplies, and a centripetal nerve through
which impressions are conveyed to be reflected to the
adjacent muscles, the glosso-pharyngeal is also a nerve
of special sensation; being the gustatory nerve, or nerve of
taste, in all the parts of the tongue to which it is distri-
buted. After many discussions, the question, which is
the nerve of taste ?—the lingual branch of the fifth, or the
glosso-pharyngeal ?—may be most probably answered by
stating that they are both nerves of this special function.
For very numerous experiments and cases have shown that
when the trunk of the fifth nerve or its lingual branch is

556 THE NERVOUS SYSTEM.

paralysed or divided, the sense of taste is completely lost in
the superior surface of the anterior and lateral parts of the
tongue. The loss is instantaneous after division of the
nerve; and, therefore, cannot be ascribed to the defective
nutrition of the part, though to this, perhaps, may be

ascribed the more complete and general loss of the sense of |

taste when the whole of the fifth nerve has been para-
lysed. ',

But, on the other hand, while the loss of taste in the
part of the tongue to which the lingual branch of the fifth
nerve is distributed proves that to be a gustatory nerve,
the fact that the sense of taste is at the same time retained
in the posterior and postero-lateral parts of the tongue,
and in the soft palate and its anterior arch, to which (and
to some parts of which exclusively) the glosso-pharyngeal
is distributed, proves that this also must be a gustatory
nerve. In a female patient at St. Bartholomew’s Hospital,
the left lingual branch of the fifth nerve was divided in
removing a portion of the lower jaw: she lost both common
sensation and the sensation of taste in the tip and the
anterior parts of the left half of the tongue, but retained
both in all the rest of the tongue. M. Lisfranc and others
have noted similar cases; and the phenomena in them
are so simple and clear, that there can scarcely be any
fallacy in the conclusion that the lingual branches of both
the fifth and the glosso-pharyngeal nerves are gustatory
nerves in the parts of the tongue which they severally
supply.

This conclusion is confirmed by some experiments on
animals, and, perhaps, more satisfactorily as concerns the
sense of taste in man, by observation of the parts of the
tongue and fauces, in which the sense is most acute. Ac-
cording to Valentin’s experiments made on thirty students,
the parts of the tongue from which the clearest sensations
of taste are derived, are the base, as far as the foramen
cecum and lines diverging forwards on each side from it ;

a eee Lae

EERE NR

a
/

y

<<) ee

THE PNEUMOGASTRIC NERVE. 557

the posterior palatine arches down to the epiglottis; the
tonsils and upper part of the pharynx over the root of the
tongue. These are the seats of the distribution of the
glosso-pharyngeal nerve. The anterior dorsal surface, and
a portion of the anterior and inferior surface of the tongue,
in which the lingual branch of the fifth is alone distributed,
conveyed no sense of taste in the majority of the subjects
of Valentin’s experiments; but even if this were generally
the case, it would not invalidate the conclusion that, in
those who have the sense of taste in the anterior and upper
part of the tongue, the lingual branch of the fifth is the
nerve by which it is exercised.

Physiology of the Pneumogastric Nerve.

The pnewmogastric nerve, nervus vagus, or par vagum (I,
fig. 151), has, of all the cranial and spinal nerves, the most
various distribution, and influences the most various func-
tions, either through its own filaments, or those which,
derived from other nerves, are mingled in its branches.

The parts supplied by the branches of the pneumogastric
nerve are as follows: by its pharyngeal branches, which
enter the pharyngeal plexus, a large portion of the mucous
membrane, and, probably, all the muscles of the pharynx;
by the superior laryngeal nerve, the mucous membrane of
the under surface of the epiglottis, the glottis, and the
greater part of the larynx, and the crico-thyroid muscle;.
by the inferior laryngeal nerve, the mucous membrane
and muscular fibres of the trachea, the lower part of the
pharynx and larynx, and all the muscles of the larynx
except the crico-thyroid ; by cesophageal branches, the
mucous membrane and muscular coats of the cesophagus. .
Moreover, the branches of the pneumogastric nerve form
a large portion of the supply of nerves to the heart and
the great arteries through the cardiac nerves, derived from
both the trunk and the recurrent nerve; to the lungs,

558 THE NERVOUS SYSTEM.

through both the anterior and the posterior pulmonary
plexuses; and to the stomach, by its terminal branches
passing over the walls of that organ; while branches are
also distributed to the liver and to the spleen.

From the parts thus enumerated as receiving nerves from
the pneumogastric, it might be assumed that this latter is
a nerve of mixed function, both sensitive and motor. Expe-
riments prove that it is so from its origin, for the irritation
of its roots, even within the cranial cavity, produces both
pain and convulsive movements of the larynx and pharynx;
and when it is divided within the skull, the same move-
ments follow the irritation of the distal portion, showing
that they are not due to reflex action. Similar experiments
prove that, through its whole course, it contains both
sensitive and motor fibres, but after it has emerged from
the skull, and, in some instances even sooner, it enters
into so many anastomoses that it is hard to say whether
the filaments it contains are, from their origin, its own, or
whether they are derived from other nerves combining
with it. This is particularly the case with the filaments
of the sympathetic nerve, which are abundantly added to
nearly all the branches of the pneumogastric. The likeness
to the sympathetic which it thus acquires is further in-
creased by its containing many filaments derived, not from
the brain, but from its own petrosal ganglia, in which
filaments originate, in the same manner as in the ganglia
of the sympathetic, so abundantly that the trunk of the
nerve is visibly larger below the ganglia than above them
(Bidder and Volkmann). Next to the sympathetic nerve,
that which most importantly communicates with the pneu-
mogastric is the accessory nerve, whose internal branch
joins its trunk, and is lost in it.

Properly, therefore, the pneumogastric might be re-

garded as a triple-mixed nerve, having out of its own,

sources, motor, sensitive, and sympathetic or ganglionic
nerve-fibres ; and to this natural complexity it adds that

|

i al — ———— aot

— ie“.

/

THE PNEUMOGASTRIC NERVE. 559

which it derives from the reception of filaments from the
sympathetic, accessory, and cervical nerves, and, probably,
the glosso-pharyngeal and facial.

The most probable account of the particular functions
which the branches of the pneumogastric nerve discharge
in the several parts to which they are distributed, may be
drawn from Dr. John Reid’s experiments on dogs. They
show that,—1. The pharyngeal branch is the principal, if
not the sole motor nerve of the pharynx and soft palate,
and is most probably wholly motor; a part of its motor
fibres being derived from the internal branch of the acces-
sory nerve. 2. The inferior laryngeal nerve is the motor
nerve of the larynx, irritation of it producing vigorous
movements of the arytenoid cartilages; while irritation of
the superior laryngeal nerve gives rise to no action in any
of the muscles attached to the arytenoid ‘cartilages, but
merely to contractions of the crico-thyroid muscle. 3. The
superior laryngeal nerve is. chiefly sensitive ; the inferior,
for the most part, motor; for division of the recurrent
nerves puts an end to the motions of the glottis, but
without lessen‘ng the sensibility of the mucous membrane ;
and division of the superior laryngeal nerves leaves the
movements of the glottis unaffected, but deprives it of its
sensibility. 4. The motions of the csophagus are depen-
dent on motor fibres of the pneumogastric, and are pro-
bably excited by impressions made upon sensitive fibres of
the same; for irritation of its trunk excites motions of the
cesophagus, which extend over the cardiac portions of the
stomach ; and division of the trunk paralyzes the ceso-
phagus, which ,then becomes distended with the food.
5. The cardiac branches of the pneumogastric nerve are
one, but not the sole channel through which the influence
of the central organs and of mental emotions is transmitted
to the heart. 6. The pulmonary branches form the prin-
cipal, but not the sole channel by which the impressions
on the mucous surface of the lungs that excite respiration,

560 THE NERVOUS SYSTEM.

are transmitted to the medulla oblongata. Dr. Reid was
unable to determine whether they contain motor fibres.

From these results, and by referring to what has been
said in former chapters, the share which the pneumogastric
nerve takes in the functions of the several parts to which
it sends branches, may be understood :—

1. In deglutition, the motions of the pharynx are of the
reflex kind. The stimulus of the food or other substance
to be swallowed, acting on the filaments of the glosso-
pharyngeal nerve as well as the filaments of the superior
laryngeal given to the pharynx, and of some other nerves,
perhaps, with which these communicate, is conducted to the
medulla oblongata, whence it is reflected, chiefly through
_ the pneumogastric, to the muscles of the pharynx.

2. In the functions of the larynx, the sensitive filaments
of the pneumogastric supply that acute sensibility by
which the glottis is guarded against the ingress of foreign
bodies, or of irrespirable gases. The contact of these
stimulates the filaments of the superior laryngeal branch
of the pneumogastric; and the impression conveyed to the
medulla oblongata, whether it produce sensation or not,
is reflected to the filaments of the recurrent or inferior
laryngeal branch, and excites contraction of the muscles
that close the glottis. Both these branches of the pneumo-
gastric co-operate also in the production and regulation
of the voice; the inferior laryngeal determining the con-
traction of the muscles that vary the tension of the vocal
cords, and the superior laryngeal conveying to the mind
the sensations of the state of these muscles necessary
for their continuous guidance. And both the branches
co-operate in the actions of the larynx in the ordinary
slight dilatation and contraction of the glottis in the acts
of expiration and inspiration, and more evidently in those
of coughing and other forcible respiratory movements

(p. 222).
3. It is partly through their influence on the sensibility

_ THE PNEUMOGASTRIC NERVE. 561

and muscular movements in the larynx, that the pneumo-
gastric nerves exercise so great an influence on the respira-
tory process, and that the division of both the nerves is
commonly fatal. To determine how death is in these cases
produced, has been the object of innumerable, and often
contradictory, experiments. It is probably produced
differently in different cases, and in many is the result of
several co-operating causes. Thus, after division of both
the nerves, the respiration at once becomes slower, the
number of respirations in a given time being commonly
diminished to one-half, probably because the pneumo-
gastric nerves are the principal conductors of the impres-
sion of the necessity of breathing to the medulla oblongata.
Respiration does not cease; for it is probable that the
impression may be conveyed to the medulla oblongata
through the sensitive nerves of all parts in which the im-
perfectly aérated blood flows (see p. 516); yet the respira-
tion being retarded, adds to the other injurious effects of
division of the nerves.

Again, division of both pneumogastric trunks, or of
both their rectrrent branches, is often very quickly fatal in
young animals; but in old animals the division of the
recurrent nerve is not generally fatal, and that of both the
pneumogastric trunks is not always fatal (J. Reid), and,
when it is so, the death ensues slowly. This difference is,
probably, because the yielding of the cartilages of the
larynx in young animals permits the glottis to be closed —
by the atmospheric pressure in inspiration, and they are
thus quickly suffocated unless tracheotomy be performed
(Legallois). In old animals, the rigidity and prominence
of the arytenoid cartilages prevent the glottis from being
completely closed by the atmospheric pressure; even when
all the muscles are paralyzed, a portion at its posterior
part remains open, and through this the animal continues
to breathe. Yet the diminution of the orifice for respira-

tion may add to the difficulty of maintaining life.
00

562 THE NERVOUS SYSTEM.

In the case of slower death, after division of both the
pneumogastric nerves, the lungs are commonly found
gorged with blood, cedematous, or nearly solid, or with a
kind of low pneumonia, and with their bronchial tubes
full of frothy bloody fluid and mucus, changes to which, in
general, the death may be proximately ascribed. These
changes are due, perhaps in part, to the influence which
the pneumogastric nerves exercise on the movements of
the air-cells and bronchi; yet, since they are not always
produced in one lung when its pneumogastric nerve is
divided, they cannot be ascribed wholly to the suspension
of organic nervous influence (J. Reid). Rather, they may
be ascribed to the hindrance to the passage of blood
through the lungs, in consequence of the diminished
supply of air and the excess of carbonic acid in the air-
cells and in the pulmonary capillaries (see p. 229); in

part, perhaps, to paralysis of the blood-vessels, leading |

to congestion; and in part, also, as the experiments of
Traube especially show, they appear due to the passage
of food and of the various secretions of the mouth and
fauces through the glottis, which, being deprived of its
sensibility, is no longer stimulated or closed in conse-
quence of their contact. He says, that if the trachea be
divided and separated from the cesophagus, or if only the
cesophagus be tied, so that no food or secretion from above
can pass down the trachea, no degeneration of the tissue
of the lungs will follow the division of the pneumogastric
nerves. So that, on the whole, death after division of the
pueumogastric nerves may be ascribed, when it occurs
quickly in young animals, to suffocation through me-
chanical closure of the paralyzed glottis: and, when it
occurs more slowly, to the congestion and pneumonia pro-
duced by the diminished supply of air, by paralysis of the
blood-vessels, and by the passage of foreign fluids into the
bronchi; and aggravated by the diminished frequency of
respiration, the insensibility to the diseased state of the

THE PNEUMOGASTRIC NERVE. 563

lungs, the diminished aperture of the glottis, and the
loss of the due nervous influence upon the process of
respiration.

4. Respecting the influence of the pneumogastric nerves
on the movements of the cesophagus and stomach, the
secretion of gastric fluid, the sensation of hunger, absorp-
tion by the stomach, and the action of the heart,* former
pages may be referred to.

Cyon and Ludwig have discovered that a remarkable
power appears to be exercised on the dilatation of the
blood-vessels by a small nerve which arises, in the rabbit,
from the superior laryngeal branch, or from this and
the trunk of the pneumogastric nerve, and after com-
municating with filaments of the inferior cervical ganglion
proceeds to the heart. If this nerve be divided, and its
upper extremity be stimulated by a weak interrupted cur-
rent, an inhibitory influence is conveyed to the vaso-motor
centre in the medulla oblongata (p. 576), so as to cause,

by reflex action, dilatation of the principal blood-vessels,

with diminution of the force and frequency of the heart’s
action. Frem the remarkable lowering of the blood-
pressure in the vessels, thus produced, this branch of the
vagus is called the depressor nerve; and. it is presumed,
as an afferent nerve of the heart, to be the means of
conveying to the vaso-motor centre in the medulla indica-
tions of such conditions of the heart as require a lowering
of the blood pressure in the vessels; as, for example,
when the heart cannot, with sufficient ease, propel blood
into the already too full or too tense arteries.

* See foot-note, p. 577.

00 2

504 _ THE NERVOUS SYSTEM.

Physiology of the Spinal Accessory Nerve.

In the preceding pages it is implied that all the motor
influence which the pneumogastric nerves exercise, is con-
veyed through filaments which, from their origin, belong
to them: and this is, perhaps, true. Yet a question, which
has been often discussed, may still be entertained, whether
a part of the motor filaments that appear to belong to
the pneumogastric nerves are not given to them from the
accessory nerves. }

The principal branch of the accessory nerve, its external
branch, supplies the sterno-mastoid and trapezius muscles;
and, though pain is produced by irritating it, it is com-
posed almost exclusively of motor fibres. It might appear
very probable, therefore, that the internal branch, which
is added to the trunk of the pneumogastric just before the
giving off of the pharyngeal branch, is also motor; and
that through it the pneumogastric nerve derives part of
the motor fibres which it supplies to the muscles enumer-
ated above. And further, since the pneumogastric nerve
has a ganglion just above the part at which the internal
branch of the accessory nerve joins its trunk, a close

analogy may seem to exist between these two nerves and:

the spinal nerves with their anterior and posterior roots.
In this view, Arnold and several later physiologists have
regarded the accessory nerve as constituting a motor root
of the vagus nerve ; and, although this view cannot now
be maintained, yet it is very probable that the accessory
nerve gives some motor filaments to the pneumogastric.
For, among the experiments made on this point, many
have shown that when the accessory nerve is irritated
within the skull, convulsive movements ensue in some of
the muscles of the larynx ; all of which, as already stated,
are supplied, apparently, by branches of the pneumo-
gastric; and (which is a very significant fact) Vrolik states
that in the chimpanzee the internal branch of the accessory

ype aged el

Come Ne at hs be 51>

) oo eay-*-

THE HYPOGLOSSAL NERVE. 565

does not join the pneumogastric at all, but goes direct to
the larynx. On the whole, therefore, although in some of
the experiments no movements in the larynx followed
irritation of the accessory nerve, yet it may be concluded
that this nerve gives to the pneumogastric some of the
motor filaments which pass, with the laryngeal branches,
to the muscles of the larynx, especially to the crico-thyroid
(Bernard) ; although it is certain that the accessory nerve
does not supply all the motor filaments which the branches
of the pneumogastric contain.

Among the roots of the accessory nerve, the lower,
arising from the spinal cord, appear to be composed ex-
clusively of motor fibres, and to be destined entirely to the
trapezius and sterno-mastoid muscles; the upper fibres,
arising from the medulla oblongata, contain many sensitive
as well as motor fibres.

Physiology of the Hypoglossal Nerve.

The hypoglossal or ninth nerve, or motor lingue, has a
peculiar relation to the muscles connected with the hyoid
bone, including those of the tongue. It supplies through
its descending branch (descendens noni), the sterno-hyoid,
sterno-thyroid, and omo-hyoid; through a special branch
the thyro-hyoid, and through its lingual branches the
genio-hyoid, stylo-glossus, hyo-glossus, and genio-hyo-
glossus and linguales. It contributes, also, to the supply
of the submaxillary gland.

The function of the hypoglossal is, probably, exclu-
sively motor. As a motor nerve, its influence on all the
muscles enumerated above is shown by their convulsions
when it is irritated, and by their loss of power when it is
paralysed. The effects of the paralysis of one hypoglossal
nerve are, however, not very striking in the tongue.
Often, in cases of hemiplegia involving the functions of
the hypoglossal nerve, it is not possible to observe any

566 THE NERVOUS SYSTEM.

deviation in the direction of the protruded tongue; pro-
bably because the tongue is so compact and firm that the

Fig. 151*

* Fig. 151. View of the nerves of the eighth pair, their distribution
and connections on the left side (from Sappey after Hirschfeld and
Leveillé). 2—z, pneumogastric nerve in the neck ; 2, ganglion of its
trunk ; 3, its union with the spinal accessory ; 4, its union with the

a eee — i

THE SYMPATHETIC NERVE. 567

muscles on either side, their insertion being nearly parallel
to the median line, can push it straight forwards or turn it
for some distance towards either side.

Physiology of the Spinal Nerves.

Little need be added to what has been already said of
these nerves (pp. 493 to 495). The anterior roots of the
spinal nerves are formed exclusively of motor fibres; the
posterior roots exclusively of sensitive fibres.

Beyond the ganglia all the spinal nerves appear to be
mixed nerves, and to contain as well sympathetic fila-
ments.

Of the functions of the ganglia of the spinal nerves
nothing very definite is known. That they are not the
reflectors of any of the ascertained reflex actions through
the spinal nerves, is shown by the reflex movements
ceasing when the posterior roots are divided between the
ganglia and the spinal cord.

PHYSIOLOGY OF THE SYMPATHETIC NERVE.

The sympathetic nerve, or sympathetic system of nerves,
obtained its name from the opinion that it is the means
through which are effected the several sympathies in

hypoglossal ; 5, pharyngeal branch ; 6, superior laryngeal nerve; 7,
external laryngeal; 8, laryngeal plexus; 9, inferior or recurrent laryn-
geal; 10, superior cardiac branch ; 11, middle cardiac ; 12, plexiform
part of the nerve in the thorax; 13, posterior pulmonary plexus ; 14,
lingual or gustatory nerve of the inferior maxillary; 15, hypoglossal,
passing into the muscles of the tongue, giving its thyro-hyoid branch,
and uniting with twigs of the lingual ; 16, glosso-pharyngeal nerve ; 17,
spinal accessory nerve, uniting by its inner branch with the pneumo-
gastric, and by its outer, passing into the sterno-mastoid muscle; 18,
second cervicle nerve ; 19, third; 20, fourth ; 21, origin of the phrenic
nerve, 22, 23, fifth, sixth, seventh, and eighth cervical nerves, forming
with the first dorsal the brachial plexus ; 24, superior cervical ganglion
of the sympathetic ; 25, middle cervical ganglion ; 26, inferior cervical
ganglion united with the first dorsal ganglion ; 27, 28, 29, 30, second,
third, fourths and fifth dorsal ganglia.

568 THE NERVOUS SYSTEM.

morbid action which distant organs manifest. It has also
been called the nervous system of organic life, upon the sup-
position, now proved erroneous, that it alone, as a nervous
system, influences the organic processes. Both terms are
defective; but, since the title sympathetic nerve has the
advantage of long and most general custom in its favour,
and is not more inaccurate than the other, it will be here
employed.

The general differences between the fibres of the cere-
bro-spinal and sympathetic nerves have been already
stated (p. 468) ; and it has been said, that although such
general differences exist, and are sufficiently discernible in
selected filaments of each system of nerves, yet they are
neither so constant, nor of such a kind, as to warrant the
supposition, that the different modes of action of the two
systems can be referred to the different structures of their
fibres. Rather, it is probable, that the laws of conduction
by the fibres are in both systems the same, and that the
differences manifest in the modes of action of the systems
are due to the multiplication and separation of the nervous
centres of the sympathetic: ganglia, or nerve-centres, being
placed in connection with the fibres of the sympathetic in
nearly all parts of their course.

According to the most general view, the sympathetic
system may be described as arranged in two. principal
divisions, each of which consists of ganglia and connecting
fibres. The first division may include those ganglia which
are seated on and involve the main trunks or branches of
cerebral and spinal nerves. This division will include the
large Gasserian ganglion on the sensitive trunk of the fifth
cerebral nerve (fig. 152), the ganglia on the glosso-pharyn-
geal and pneumogastric nerves, and the ganglia on the
posterior or sensitive branches of the spinal nerves (fig. 141):

To the second division belong the double chain of pra-
vertebral ganglia (24 to 30, fig. 151) and their branches,
extending from the interior and base of the skull to the

i a alae

eee

THE SYMPATHETIC NERVE. 569

coccyx; the various sympathetic visceral plexuses and

Fig. 152.*

* Fig. 152. General plan of the branches of the fifth pair (after a
sketch by Charles Bell). 4.—1, lesser root of the fifth pair ; 2, greater
root passing forwards into the Gasserian ganglion ; 3, placed on the |
bone above the ophthalmic nerve, which is seen dividing into the supra-
orbital, lachrymal, and nasal branches, the latter connected with the
ophthalmic ganglion ; 4, placed on the bone close to the foramen rotun-
dum, marks the superior maxillary division, which is connected below
with the spheno-palatine ganglion, and passes forwards to the infra-
orbital foramen ; 5, placed on the bone over the foramen ovale, marks
the submaxillary nerve, giving off the anterior auricular and muscular
branches, and continued by the inferior dental to the lower jaw, and by
the gustatory to the tongue ; a, the submaxillary gland, the submax-
illary ganglion placed above it in connection with the gustatory nerve ;
6, the chorda tympani; 7, the facial nerve issuing from the stylo-
mastoid foramen.

570 THE NERVOUS SYSTEM.

their ganglia, as the cardiac, the solar, the renal and hypo-
gastric plexuses; and in the same division may be included
the ganglia in the neighbourhood of the head and neck,
namely, the ophthalmic or lenticular, the spheno-palatine,
the otic, and the submaxillary ganglia (fig. 152).

The structure of all these ganglia appears to be essen-
tially similar, all containing—tst, nerve-fibres traversing
them; 2ndly, nerve-fibres originating in them; ‘3rdly,
nerve- or ganglion-corpuscles, giving origin to these fibres;
and 4thly, other corpuscles that appear free. And in the
trunk, and thence proceeding branches of the sympathetic,
there appear to be always—tst, fibres which arise in its
own ganglia; 2ndly, fibres derived from the ganglia of
the cerebral and spinal nerves; 3rdly, fibres derived from
the brain and spinal cord and transmitted through the
roots of their nerves. The spinal cord, indeed, appears
to furnish a large source of the fibres of the sympathetic
nerve.

' Respecting the course of the filaments belonging to the
sympathetic, the following appears to have been deter-

mined. Of the filaments derived from the ganglia on the ~

cerebral nerves, some may pass towards the brain; for, in
the trunks of the nerves, between the ganglia and the
brain, fine filaments like those of the sympathetic are
found. But these may be proceeding from the brain to
the ganglia; and, on the whole, it is probable that nearly
all the filaments originating in the ganglia or cerebral
nerves, go out towards the tissues and organs to be sup-
plied, some of them being centrifugal, some centripetal ;
so that each ganglion with its outgoing filaments may form
a kind of special nervous system appropriated to the part
in which its filaments are placed. Such, for example, may
be the ophthalmic ganglion with the ciliary nerves, con-
nected with the brain and the rest of the ‘sympathetic

system by the branches of the third, fifth, and sympa- —

thetic nerves that form its roots, yet, by filaments of its

OE SE Ny ae ies a nteapamlnales

THE SYMPATHETIC NERVE. 571

own, controlling, in some mode and degree, the processes
in the interior of the eye.

Of the fibres that arise in tHe spinal ganglia, some
appear to pass into the posterior branches of the spinal
nerves, and to be distributed with them; the rest pass
through the branches by which the spinal nerves commu-
nicate with the trunks of the sympathetic, and then entering
the sympathetic, are distributed with its branches to the
viscera. With these, also a certain number of the large
ordinary cerebro-spinal nerve-fibres, after traversing the
ganglia, pass into the sympathetic.

Of the fibres derived from the ganglia of the sympa-
thetic itself, some go straightway towards the viscera, the
rest pass through the branches of communication between
the sympathetic and the branches of the spinal nerves,
and joining these spinal nerves, proceed with them to their
respective seats of distribution, especially to the more
- sensitive parts.

Thus, through these communicating branches, which
have been generally called roots or origins of the sympa-
thetic nerve, an interchange is effected between all the
spinal nerves and the sympathetic trunks; all the ganglia,
also, which are seated on the cerebral nerves, have roots
(as they are called) through which filaments of the cere-
bral nerves are added to their own. So that, probably,
all sympathetic nerves contain some intermingled cerebral
or spinal nerve-fibres; and all cerebral and spinal nerves
some filaments derived from the sympathetic system or
from ganglia. But the proportions in which these fila-
ments are mingled are not uniform. The nerves which
arise from the brain and spinal cord retain throughout
their course and distribution a preponderance of cerebro-
spinal fibres, while the nerves immediately arising from
the so-called sympathetic ganglia probably contain a
majority of sympathetic fibres. But inasmuch as there is
no certainty that in structure the branches of cerebral

572 THE NERVOUS SYSTEM. |

or spinal nerves differ always from those of the sympathetic
system, it is impossible in the present state of our know-
ledge to be sure of the source of fibres which from their
structure might lead the observer to believe that they arose
from the brain or spinal cord on the one hand, or from
the sympathetic ganglia on the other... In other words,
although the large white tubular fibres are especially cha-
racteristic of cerebro-spinal nerves, and the pale or
gelatinous fibres of a sympathetic nerve, in which they
largely preponderate, there is no certainty to be obtained
in a doubtful case, of whether the nerve-fibre is derived
from one or the other, from mere examination of its struc-
ture. It may be derived from either source.

With respect to the functions of the sympathetic nervous
system, it may be stated generally that the sympathetic
nerve-fibres are simple conductors of impressions, as those
of the cerebro-spinal system are, and that the ganglionic
centres have (each in its appropriate sphere) the like
powers both of conducting and of communicating impres-
sions. Their power of conducting impressions is suffi-
ciently proved in ordinary diseases, as when any of the
viscera, usually unfelt, give rise to sensations of pain, or
when a part not commonly subject to mental influence is
excited or retarded in its actions by the various conditions
of the mind; for in all these cases impressions must be
conducted to and fro through the whole distance between
the part and the spinal cord and brain. So, also, in
experiments, now more than sufficiently numerous, irrita-
tions of the semilunar ganglia, the splanchnic nerves, the
thoracic, hepatic, and other ganglia and nerves, have elicited
expressions of pain, and have excited movements in the
muscular organs supplied from the irritated part.

In the case of pain excited, or movements affected by —
the mind, it may be supposed that the conduction of im-
pressions is effected through the cerebro-spinal fibres
which are mingled in all, or nearly all, parts of the sym-

ipa ire

— os

THE SYMPATHETIC NERVE. 573

pathetic nerves. There are no means of deciding this; but
if it be admitted that the conduction is effected through
the cerebro-spinal nerve-fibres, then, whether or not they
pass uninterruptedly between the brain or spinal cord and
the part affected, it must be assumed that their mode of
conduction is modified by the ganglia. For, if such cere-
bro-spinal fibres are conducted in the ordinary manner,
the parts should be always sensible and liable to the in-
fluence of the will, and impressions should be conveyed to
and fro instantaneously. But this is not the case; on the
contrary, through the branches of the sympathetic nerve
and its ganglia, none but intense impressions, or impres-
sions exaggerated by the morbid excitability of the nerves
or ganglia, can be conveyed.

Respecting the general action of the ganglia of the
sympathetic nerve, little need be said here, since they may
be taken as examples by which to illustrate the common
modes of action of all nerve-centres (see p. 483). Indeed,
complex as the sympathetic system, taken as a whole, is,
it presents in each of its parts a simplicity not to be found
in the cerebio-spinal system: for each ganglion with
afferent and efferent nerves forms a simple nervous system,
and might serve for the illustration of all the nervous
actions with which the mind is unconnected. But it will
be more convenient. to consider the ganglia now in connec-
tion with the functions that they may be supposed to con-
trol, in the several organs supplied by the sympathetic

system alone, or in conjunction with the cerebro-spinal.

The general processes which the sympathetic appears to
influence, are those of involuntary motion, secretion, and
nutrition. ‘

Many movements take place involuntarily in parts sup-
plied with cerebro-spinal nerves, as the respiratory and
other spinal reflex motions; but the parts principally
supplied with sympathetic nerves are usually capable of

574. THE NERVOUS SYSTEM.

none but involuntary movements, and when the mind acts
on them at all, it is only through the strong excitement or
depressing influence of some passion, or through some
voluntary movement with which the actions of the involun-
tary part are commonly associated. The heart, stomach,
and intestines are examples of these statements; for the
heart and stomach, though supplied in large measure from
the pneumogastric nerves, yet probably derive through
them few filaments except such as have arisen from their
ganglia, and are therefore of the nature of sympathetic
fibres.

The parts which, are supplied with motor power by the
sympathetic nerve continue to move, though more feebly
than .before, when they are separated from their natural
connections with the rest of the sympathetic system, and
wholly removed from the body. Thus, the heart, after it
is taken from the body, continues to beat in Mammalia for
one or two minutes, in reptiles and Amphibia for hours ;
and the peristaltic motions of the intestine continue under
the same circumstances. Hence the motion of the parts
supplied with nerves from the sympathetic are shown to
be, in a measure, independent of the brain and spinal
cord. |

It seems to be a general rule, at least in animals that
have both cerebro-spinal and sympathetic nerves much de-
veloped, that the involuntary movements excited by stimuli
conveyed through ganglia are orderly and like natural
movements, while those excited through nerves without
ganglia are convulsive and disorderly ; and the probability
is that, in the natural state, it is through the same ganglia
that natural stimuli, impressing centripetal nerves, are
reflected through centrifugal nerves to the involuntary
muscles. As the muscles of respiration are maintained
in uniform rhythmic action chiefly by the reflecting and
combining power of the medulla oblongata, so, probably,
are those of the heart, stomach, and intestines, by their

4%

Ape aerated:

THE SYMPATHETIC NERVE. 575

several ganglia. And as with the ganglia of the sympa-
thetic and their nerves, so with the medulla oblongata and
its nerves distributed to respiratory muscles,—if these
nerves or the medulla oblongata itself be directly stimu-
lated, the movements that follow are convulsive and.
disorderly ; but if the medulla be stimulated through a
centripetal nerve, as when cold is applied to the skin, then
the impressions are reflected so as to produce movements
which, though they may be very quick and almost con-
vulsive, are yet combined in the plan of the proper res-
piratory acts.

Among the ganglia of the sympathetic nerves to which
this co-ordination of movements is to be ascribed, must be
reckoned, not those alone which are on the principal trunks
and branches of the sympathetic external to any organ,
but those ‘also which le in the very substance of the
organs; such as those discovered in the heart by Remak.
Those also may be included which have been found in the
mesentery close by the intestines, as well as in the sub-
mucous tissue of the stomach and intestinal canal (Meiss-
ner), and in other parts. The extension of discoveries
of such ganglia will probably diminish yet further the
number of instances in which the involuntary movements
appear to be effected independently of central nervous
influence.

Respecting the influence of the sympathetic nerve in
nutrition and secretion, we may refer to the chapters on
those processes.

The influence of the Soma nerves on the blood-
vessels has been already referred to in the Section on the
Arteries. It was stated that the muscular tissue of the
blood-vessels were supplied by sympathetic nerve-branches,
called from their distribution and function vaso-motor
nerves; and that by these the condition of the vessels with
respect to contraction or relaxation, and therefore to the
stream of blood which flowed through them in a given

576 THE NERVOUS SYSTEM.

time, is governed. When these vaso-motor nerves are
intact, the muscular tissue of the arteries is always in a
state of tonic contraction, which varies in degree at
different times. When they are divided, the muscular
fibres in which they are distributed are paralyzed, and the
blood-vessels become dilated. The most usual experiment
in illustration of , these facts is performed by exposing in a
rabbit the cervical sympathetic, from which vaso-motor
branches are given to the blood-vessels of the head and
neck. On dividing the nerve, the blood-vessels of the
same side are paralyzed, and the stream of blood, now un-
controlled, dilates them. The effect is best seen in the ear,
the blood-vessels of which become manifestly larger than
those of the opposite side; while the part becomes redder
and warmer from the increased quantity of blood circu-
lating through it. On galvanizing the upper divided
extremity of the nerve, the muscular fibres of the blood-
vessels respond to the stimulus by again contracting, and the
parts become paler, colder, and less sensitive than natural.

The vaso-motor nerves arise directly from the sympa-
thetic. Thus the blood-vessels of the head and neck are
supplied by branches from the superior cervical ganglion,
those of the thorax from the cervical and upper dorsal
ganglia, those of the abdomen chiefly by the splanchnic
nerves, and so forth. But it is now generally agreed, from
the results of experiments by Ludwig and others, that the
principal vaso-motor nerve-centre, with which all these nerves
communicate, and by which their action is regulated, is
situate in the medulla oblongata—or, in other words, that
the vaso-motor fibres, arising from this nerve-centre, pass
down the spinal cord, and issuing by the anterior roots of
the spinal nerves, enter the various ganglia on the pree-
vertebral cord of the sympathetic, and thence reach their
destination, probably taking with them fibres which arise
in the ganglia through which they pass. The vaso-motor
centre in the medulla appears to have a regulating power

7 = ft. ta”

Ser 17 eT Se ll

THE SYMPATHETIC NERVE. 577

over the whole of the vaso-motor nerves; but it seems
likely that other secondary vaso-motor centres may exist
in ganglia in different parts of the body, and may be the
centres by which, under ordinary circumstances, vaso-
motor changes are regulated in the territory in which they
are placed. .

The vaso-motor nerve-centres are not only centres from
which influences are directly transmitted to the blood-
vessels, but, like other nerve-centres, may be the means by
which impulses are reflected (p. 486). And reflex actions
occur in connection with the muscular fibres of blood-ves-
sels, as with those of the voluntary muscles. Such reflected
impressions may lead either to contraction or to dilatation
of blood-vessels ; or, in other words, the action may be eacito-
vaso-motor, or vaso-inhibitory. The most remarkable
instance at present known of a nerve, the stimulation of
which leads by reflex action through the vaso-motor centre

in the medulla oblongata, to dilatation of blood-vessels,

is the depressor branch of the vagus (p. 563); but similar
effects have been observed in a less degree, on stimulating
other afferent spinal nerves.*

It is, of course, very difficult to determine the relative
share exercised by the true sympathetic and the ordinary
cerebro-spinal fibres in the contraction of blood-vessels,
and in the general processes of nutrition and secretion,
since both kinds of fibres appear to be distributed to most
parts, and there seems to be no possibility of isolating
them. Probably the safest view of the question at present
is, still to regard all the processes of organic life, in
man, as liable to the combined influences of the cere-
bro-spinal and the sympathetic systems; to consider that
those influences may be so combined as that the sympa-

* For an admirable summary of what is at present known regarding
the Innervation of the Heart and Blood-vessels, see Lectures by Dr.
Rutherford, in the ‘‘ Lancet,” December 16, 1871, and January 20,

1872.
PP

578 THE NERVOUS SYSTEM. —

thetic nerves and ganglia may be in man, as in the lower : >

animals, the parts through which the ordinary and constant
influence of nervous force is exercised on the organic
processes; while the cerebro-spinal nervous centres and
their ganglia are so closely connected with the proper
sympathetic ganglia, that neither of them can be said to
be independent of the other; each, as a rule, and under
ordinary circumstances, governing its own domain, but
always liable to be influenced by the other.

CHAPTER XVII.
CAUSES AND PHENOMENA OF MOTION.

THE most evident vital motions observable in the bodies
of animals, are performed in one or other of the following
ways: first, by means of the oscillatory motion or vibration
of microscopic cilia, with which the surfaces of certain
membranes are beset ; and secondly, by the contraction of
fibres which either have a longitudinal direction and are
fixed at both extremities, or form circular bands: the con-
traction or shortening of the fibres bringing the parts to
which they are fixed nearer to each other. There are,
besides, various molecular movements allied to those which
need not here be considered.

CILIARY MOTION.

Ciliary motion consists in the incessant vibration of fine,
pellucid, blunt processes, about -,!,, of an inch long,
termed cilia (figs. 153, 154), situated on the free extremi-
ties of the cells of epithelium covering certain surfaces of
the body.

The distribution and structure of ciliary epithelium —
and the microscopic appearances of cilia in motion have ~
been already described (p. 33).

CILIARY MOTION. 579

‘Ciliary motion seems to be alike independent of the will,
of the direct influence of the nervous system, and of muscular
contraction, for it is involuntary; there is no nervous or
muscular tissue in the immediate neighbourhood of the
cilia, and it continues for several hours after death or
removal from the body, provided the portion of tissue
under examination be kept moist. Its independence of
the nervous system is shown also in its occurrence in the

Fig. 153.*

lowest invertebrate animals apparently unprovided with
anything analogous to a nervous system, in its persistence
in animals killed by prussic acid, by narcotic or other
poisons, and after the direct application: of narcotics to
the ciliary surface, or the discharge of a Leyden jar, or
of a galvanic shock through it. The vapour of chloroform
arrests the motion; but it is renewed on the. discon-
tinuance of the application (Lister). According to Kuhne,
the movement ceases in an atmosphere deprived of oxygen,
‘but is revived on the admission of this gas. Carbonic
acid stops the movement. The contact of various substances
will stop the motion altogether; but this seems to depend
‘chiefly on destruction of the delicate substance of which
the cilia are composed.

Little or nothing is known with certainty regarding
the nature of ciliary action. As Dr. Sharpey observes,

* Fig. 153. Spherdidal ciliated cells from the mouth of the frog ;
magnified 300 diameters (Sharpey).

+ Fig. 154. Columnar ciliated epithelium cells from the human
nasal membrane ; magnified 300 diameters (Sharpey).

EN

PP2

580 MOTION.

however, it is a special manifestation of a similar pro-
perty to that by which the other motions of animals are
effected, namely, by what we term vital contractility. The
fact of the more evident movements of the larger animals
being effected by a structure apparently different from
that of cilia, is no argument against such a supposition.
For, if we consider the matter, it will be plain that our
prejudices against admitting a relationship to exist between
the two structures, muscles and cilia, rests on no definite
ground; and for the simple reason, that we know so little
of the manner of production of movement in either case.
The mere difference of structure is not an argument in
point; neither is the presence or absence of nerves. The
movements of both muscles and cilia are manifestations of
force, by certain special structures, which we call respec-
tively muscles and cilia. We know nothing more about
the means by which the manifestation. is effected by one of
these structures than by the other ; and the-mere fact that
one has nerves and the other has not, is no more argument
against cilia having what we call a vital power of contrac-
tion, than the presence or absence of stripes from voluntary
or involuntary muscles respectively, is an argument for
or against the contraction of one of them being vital and
the other not so. Inasmuch then as cilia are found in
living structures only, and inasmuch as they are a means.
whereby force is transformed (see Chap. II.), their peculiar
properties have as much right to be invested with the
term vital as have those of muscular fibres. The term
may be in both instances a bad one,—it certainly is an
unsatisfactory one,—but it is as good for one case as the
other.
| MUSCULAR MOTION.

There are two chief kinds of muscular tissue, the striped,
and the plain or wnstriped, and they are distinguished by
structural peculiarities and mode of action. The striped
form of muscular fibre is sometimes called voluntary muscle,

t
2
(
i

CILIARY AND MUSCULAR MOTION. 581

because all muscles under the control of the will are con-
structed of it. The plain or unstriped variety is often
termed involuntary, because it alone is found in the greater
number of the muscles over which the will has no power.
The involuntary or unstriped muscles are made up,
according to Kolliker, of elongated, spindle-shaped, nu-
cleated jfibre-cells (fig. 155), which in their most perfect
form are flat, from about ;,, to 3), of an inch broad,
and about ;1, to ;+, of an inch in length,—very clear,
granular, and brittle, so that when they break, they often
have abruptly rounded or square extremities. Each fibre-

Fig. 155.* Fig. 156.+

cell possesses an elongated nucleus, and many are marked
along the middle, or, more rarely, along one of the edges,

* Fig. 155. Muscular fibre-cells from human arteries, magnified
350 diameters (K6lliker). «@, natural state; 0, treated with acetic
acid.

} Fig. 156. Plain muscular fibres from the human bladder, mag-

- nified 250 diameters. «a, in their natural state; 0, treated with acetic

acid to show the nuclei.

582 MOTION.

either by a fine continuous dark streak, or by short iso-
lated dark lines, or by dark points arranged in a row, or
scattered. These fibre-cells, by their union, form fibres
and bundles of fibres (fig. 156). The fibres have no
distinct sheath.

The fibres of involuntary muscle, such as are here
described, form the proper muscular coats of the
digestive canal from the middle of the cesophagus to
the internal sphincter ani, of the ureters and urinary
bladder, the trachea and bronchi, the ducts of glands,
the gall bladder, the vesiculz seminales, the pregnant
uterus, of blood-vessels and lymphatics, the iris, and some.
other parts.

This form of tissue also enters largely into the compo-
sition of the tunica dartos, and is the principal cause of
the wrinkling and contraction of the scrotum on exposure
to cold. The fibres of the cremaster assist in some measure
in producing this effect, but they are chiefly concerned in
drawing up the testis and its coverings towards the inguinal
opening. Unstriped muscular tissue occurs largely also
in the cutis (p. 421),
being especially abun-
dant at the interspaces
between the bases of
the papille. Hence,
when it contracts under.
the influence of cold,
fear, electricity, or any
other stimulus, the
papille are made un-
usually prominent, and give rise to the peculiar rough-

Fig. 157.*

* Fig. 157. Perpendicular section through the scalp, with two hair-
sacs ; a, epidermis; b, cutis; c, muscles of the hair-follicles (after
Kolliker).

Spee,

oe eee”

STRUCTURE OF UNSTRIPED MUSCLE. 583

ness of the skin termed cutis anserina, or. goose-skin. It
occurs also in the superficial portion of the cutis, in all
parts where hairs occur, in the form of flattened roundish
bundles, which lie alongside the hair-follicles and sebaceous
glands. They pass obliquely from without inwards, em-
brace the sebaceous glands, and are attached to the hair
follicles near their base (fig. 157).

To this kind of muscular fibre the term organic is often
applied, from the fact that it enters especially into the
construction of such parts as are concerned in what has been
called organic life (see note, p. 464).

The muscles of animal life, or striped muscles, include the
whole class of voluntary muscles, the heart, and those
muscles neither completely voluntary nor involuntary, which
form part of the walls of the pharynx, and exist in many
other parts of the body, Fig. 158.*
as the internal ear, ure-
thra, etc. All these
muscles are composed
of fleshy bundles called
fasciculi, enclosed in
coverings of fibro-cellu-
lar tissue, by which each
is at once connected
with, and isolated from,
those adjacent to it (fig. 158). Each-bundle is again

divided into smaller ones, similarly ensheathed and simi-

larly divisible; and so on, through an uncertain number
of gradations, till one arrives at the primitive fasciculi, or
the muscular fibres peculiarly so called.

* Fig. 158. A small portion of muscle, natural size, consisting of
larger and smaller fasciculi, seen in a transverse section, and the same
magnified 5 diameters (after Sharpey. )

584 MOTION.

Muscular jibres consist, each of them, of a tube or sheath
of delicate structureless membrane, called the sarcolemma,
enclosing a number of filaments or /ibrils. They are
cylindriform or prismatic,
with five or more sides,
according to the manner in
which they are compressed
by adjacent fibres. Their
average diameter is about
sty of an inch, and their length never exceeds an inch
and a half.

Each muscular fibre is thus constructed :—Externally
is a fine, transparent, struc-
tureless membrane, called
the sarcolemma, which in
the form of a tubular in-
vesting sheath forms the
outer wall of the fibre, and
is filled by the contractile
material of which the fibre
is chiefly made up. Some-
times, from its comparative
toughness, the sarcolemma
will remain untorn, when
by extension the contained
part can be broken (fig.
159), and its presence is
in this way best demonstrated. The fibres, which are
cylindriform or prismatic, with an average diameter of
about 51, of an inch, are of a pale yellow colour, and
apparently marked by fine strize, which pass transversely

Fig. 159.*

Fig. 160.F

OM 1)

7

yj

f/f
wy,

)
47,
yy)

MY,

DP
1
{/

i)

yg

S\)
LIT;

\\
Udy

Nini
tif
o

yy

A

SS
>=
SS
SS

* Fig. 159. Muscular fibre torn across; the sarcolemma still con-
necting the two parts of the fibre (after Todd and Bowman).

7 Fig. 160. A few muscular fibres, being part of a small fasciculus,
highly magnified, showing the transverse strie. a, end view of J, 4,
fibres ; c, a fibre split into its fibrils (after Sharpey).

SS

STRUCTURE OF STRIPED MUSCLE. 585

round them, in slightly curved or wholly parallel lines.
Other, but generally more obscure strice, ‘also pass
longitudinally over the tubes, and indicate the direction
of the filaments or primitive jibrils of which the substance
of each fibre is composed (fig. 160).
The whole substance of the fibre contained within the
sarcolemma may be thus supposed to be constructed of
longitudinal fibrils—a bundle of fibrils surrounded by the

sarcolemma constituting a fibre.
Fig. 161.*

e-)

Hy a
Wnaa,,
a, eS
PEC aay va

i
Fy
Te,

Q

Wai.

3

f

fae,
’
H
?

Rae

There is still some doubt regarding the nature of the
fibrils. Each of them appears to be composed of a single
row of minute dark quadrangular particles called sarcous

* Fig. 161. A. Portion of a medium-sized human muscular fibre,
magnified nearly 800 diameters. B. Separated bundles of fibrils equally
magnified ; a, a, larger, and b, b, smaller collections ; c, still smaller ;
d, d, the smallest which could be detached, possibly representing a

single series of sarcous elements (after Sharpey). —

586 MOTION.

elements, which are separated from each other by a bright
space formed of a pellucid substance continuous with
them. A fine streak can be sometimes discerned passing
across the bright interval between the sarcous elements.
Dr. Sharpey believes that, even in a fibril so constituted,
the ultimate anatomical element of the fibre has not been
isolated. He believes that each fibril with quadrangular |
sarcous elements is composed of a number of other fibrils
still finer, so that the sarcous element of an ultimate fibril
would be not quadrangular but as a streak, and the dark
transverse streak on the bright space but a row of dots. In
either case the appearance of striation in the whole fibre
would be produced by the arrangement, side by side, of the
dark and light portions respectively of the fibrils (fig. 161).
Although each muscular fibre may be considered to be
formed of a number of longitudinal fibrils, arranged side
by side, it is also true that they are not naturally separate
from each other, there being lateral cohesion, if not fusion,
of each sarcous element with those around and in contact
with it; so that it happens that there is a tendency for a
Fig. 162.* fibre to split, not only into separate fibrils,
but also occasionally into plates or disks,
each of which is composed of sarcous ele-
ments laterally adherent one to another.
The muscular fibres of the heart, although
striped and resembling closely those of the
voluntary muscles in their general structure,
present these distinctions :—They are finer
and more faintly striated, they branch and
anastomose one with another, and no sarco-
lemma can be usually discerned (fig. 162).
The voluntary,muscles are freely supplied with blood-
vessels; the capillaries form a network with oblong meshes

* Fig. 162. Muscular fibres from the heart, magnified, showing their »
cross-striz, divisions and junctions (from Kolliker).

MUSCULAR FIBRES OF THE HEART. 587

around the fibres on the outside of the sarcolemma.
No vessels penetrate the sarcolemma to enter the interior
of the fibre.

Nerves also are supplied freely to muscles; the volun-
tary muscles receiving chiefly nerves from the cerebro-
spinal system, and the unstriped muscles from the sym-
pathetic or ganglionic system.

Properties of Muscular Tissue.

The property of muscular tissue, by which its peculiar
functions are exercised, is its contractility, which, in
the contraction or shortening of muscle, is excited by all
kinds of stimuli, applied either directly to the muscles, or
indirectly to them through the medium of their motor
nerves. This property, although commonly brought into
action through the nervous system, is inherent in the mus-
cular tissue. For—trst, it may be manifested in a muscle
which is isolated from the influence of the nervous system
by division of the nerves supplying it, so long as the natural
tissue of the muscle is duly nourished; and 2ndly, it is
manifest in a portion of muscular fibre,in which, under
the microscope, no nerve-fibre can be traced.

If the removal of nervous influence be long continued,
as by division of the nerve supplying a muscle, or in cases
of paralysis of long-standing, the irritability, i.e., the
power of both perceiving and responding to a stimulus,
may be lost; but probably this is chiefly due to the
impaired nutrition of the muscular tissue, which ensues
through its inaction (J. Reid). The irritability of muscles
is also of course soon lost, unless a supply of arterial blood
to them is kept up. Thus, after ligature of the main
arterial trunk of a limb, the power of moving the muscles
is partially or wholly lost, until the collateral circulation is
established ; and when, in animals, the abdominal aorta is
tied, the hind legs are rendered almost powerless (Segalas).
So, also, it is to the imperfect supply of arterial blood to

588 "MOTION, © |

the muscular tissue of the heart, that the cessation of the
action of this organ in asphyxia is in some measure due
(p- 231).

Besides the property of contractility, the muscles, espe-
cially the striated or those of animal life, possess sensibility
by means of the sensitive nerve-fibres distributed to them.
The amount of common sensibility in muscles is not great ;
for they may be cut or pricked without giving rise to
severe pain, at least in their healthy condition. But they
have a peculiar sensibility, or at least a peculiar modifi-
cation of common sensibility, which is shown in that their
nerves can communicate to the mind an accurate knowledge
of their states and positions when in action. By this sensi-
bility, we are not only made conscious of the morbid sensa-
tions of fatigue and cramp in muscles, but acquire, through
muscular action, a knowledge of the distance of bodies and
their relation to each other, and are enabled to estimate and
compare their weight and resistance by the effort of which
we are conscious in measuring, moving, or raising them.
Except with such knowledge of the position and state of
each muscle, we could not tell how or when to move it for
any required action; nor without such a sensation of effort
could we maintain the muscles in contraction for any pro-
longed exertion.

The mode of contraction in the transversely-striated mus-
cular tissue, has been much disputed. The most probable
account, which has been especially illustrated by Mr.
Bowman, is that the contraction is effected by an approxi-
mation of the constituent parts of the fibrils, which, at the
instant of contraction, without any alteration in their
general direction, become closer, flatter, and wider; a con-
dition which is rendered evident by the approximation of
the transverse striz seen on the surface of the fasciculus,

and by its increased breadth and thickness. The appear-—

ance of the zigzag lines into which it was supposed the
fibres are thrown in contraction, is due to the relaxation of

i
%
7.

CONTRACTION IN STRIATED MUSCLES. 589 ©

a fibre which has been recently contracted, and is not at
once stretched again by some antagonist fibre, or whose
extremities are kept close together by the contractions of
other fibres. The contraction is therefore a simple, and,
according to Ed. Weber, an uniform, simultaneous, and
steady shortening of each fibre and its contents. What
each fibril or fibre loses in length, it gains in thickness :
the contraction is a change of form not of size; it is, there-
fore, not attended with any diminution in bulk, from con-
densation of the tissue. This has been proved for entire
muscles, by making a mass of muscle, or many fibres to-
gether, contract in a vessel full of water, with which a fine,
perpendicular, graduated tube communicates. Any dimi-
nution of the bulk of the contracting muscle would be
attended by a fall of fluid in the tube; but when the ex-
periment is carefully performed, the level of the water in
the tube remains the same, whether the muscle be con-
tZacted or not.* .

In thus shortening, muscles appear to swell up, becom-
ing rounder, more prominent, harder, and apparently
tougher. But this hardness of muscle in the state of con-
traction, is not due to increased firmness or condensation of
the muscular tissue, but to the increased tension to which
the fibres, as well as their tendons and other tissues, are
subjected from the resistance ordinarily opposed to their
contraction. When no resistance is offered, as when a
muscle is cut off from its tendon, not only is no hardness
perceived during contraction, but the muscular tissue is
even softer, more extensile, and less elastic than in its
ordinary uncontracted state (Ed. Weber).

Heat is developed in the contraction of muscles. Bec-
querel and Breschet found, with the thermo-multiplier,

* Edward Weber, however, states that a very slight diminution does
take place in the bulk of a contracting muscle; but it is so slight as to
be practically of no moment.

590 - MOTION.

about 1° of heat produced by each forcible contraction of a
man’s biceps; and when the actions were long continued,
the temperature of the muscle increased 2°. It is not
known whether this development of heat is due to chemi-
cal changes ensuing in the muscle, or to the friction of its
fibres vigorously acting: in either case, we may refer to it
a part of the heat developed in active exercise (p. 233).
And Nasse suspects that to it is due the higher tempera-
ture of the blood in the left ventricle; for he says that
this fluid is always warmer in the left ventricle than in the
left auricle, and that the blood in the latter is but little
warmer than that on the right side of the heart. But these
experiments need confirmation.

Sound is said to be produced when muscles contract for-
cibly. Dr. Wollaston showed that this sound might be
easily heard by placing the tip of the little finger in the
ear, and then making some muscles contract, as those of
the ball of the thumb, whose sound may be conducted to
the ear through the substance of the hand and finger.
A low shaking or rumbling sound is heard, the height
and loudness of the note being in direct proportion to
the force and quickness of the muscular action, and to
the number of fibres that act together, or, as it were, in
time.

The two kinds of fibres, the striped and unstriped, fat
characteristic differences in the mode in which they act on -
the application of the same stimulus; differences which
may be ascribed in great part to their respective differences
of structure, but to some degree possibly, to their respec-
tive modes of connection with the nervous system. When
irritation is applied directly to a muscle with striated
fibres, or to the motor nerve supplying it, contraction of
the part irritated, and of that only, ensues; and this
contraction is instantaneous, and ceases on the instant
of withdrawing the irritation. But when any part with
unstriped muscular fibres, e.g., the intestines or bladder, is

6 age Ie

SOUND OF MUSCULAR CONTRACTION. 591

irritated, the subsequent contraction ensues more slowly,
extends beyond the part irritated, and with alternating
relaxation, continues for some time after the withdrawal
of the irritation. Ed. Weber particularly illustrated the
difference in the modes of contraction of the two kinds of
muscular fibres by the effects of the electro-magnetic
stimulus. The rapidly succeeding shocks given by this
means to the nerves of muscles excite in all the trans-
versely-striated muscles a fixed state of tetanic contraction,
which lasts as long as the stimulus is continued, and on
its withdrawal instantly ceases: but in the muscles with
smooth fibres they excite, if any movement, only one that
ensues slowly, is comparatively slight, alternates with rest,
and continues for a time after the stimulus is withdrawn.

In their mode of responding to these stimuli, all the
voluntary muscles, or those with transverse strie, are
alike ; but among those with plain or unstriped fibres
there are many differences,—a fact which tends to confirm
the opinion that their peculiarity depends as well on their
connection with nerves and ganglia as on their own pro-
perties. Acccrding to Weber, the ureters and gall-bladder
are the parts least excited by stimuli: they do not act at
all till the stimulus has been long applied, and then contract
feebly, and to a small extent. The contractions of the
cecum and stomach are quicker and wider-spread : still
quicker those of the iris; and of the urinary bladder if it be
not too full. The actions of the small and large intestines,
of the vas deferens, and pregnant uterus, are yet more
vivid, more regular, and more sustained; and they require
no more stimulus than that of the air toexcite them. The
heart is the quickest and most vigorous of all the muscles
of organic life in contracting upon irritation, and appears
in this, as in nearly all other respects, to be the connecting
member of the two classes of muscles.

All the muscles retain their property of contracting un-
der the influence of stimuli applied to them or to their

592 MOTION.

nerves for some time after death, the period being longer
in cold-blooded than in warm-blooded Vertebrata, and
shorter in birds than in Mammalia. It would seem as if
the more active the respiratory process in the living animal,
the shorter is the time of duration of the irritability in the
muscles after death; and this is confirmed by the comparison
of different species in the same order of Vertebrata. But
the period during which this irritability lasts, is not the
same in all persons, nor in all the muscles of the same
persons. In aman it ceases, according to Nysten, in the
following order :—first in the left ventricle, then in the

intestines and stomach, the urinary bladder, right ventricle,

cesophagus, iris; then in the voluntary muscles of the
trunk, lower and upper extremities; lastly in the right
and left auricle of the heart.

After the muscles of the dead body ‘have lost their irri-
tability or capability of being excited to contraction by the
application of a stimulus, they spontaneously pass into a
state of contraction, apparently identical with that which
ensues during life.* It affects all the muscles of the body;
and, where external circumstances do not prevent it, com-
monly fixes the limbs in that which is their natural posture

of equilibrium or rest. Hence, and from the simultaneous .

contraction of all the muscles of the trunk, is produced a
general stiffening of the body, constituting the rigor mortis
or post-mortem rigidity.+ :

* If, however, arterial blood be made to circulate through the body
or through a limb, the post-mortem contraction of the muscles thus sup-
plied with blood, may, as Dr. Brown-Séquard has shown, be suspended,
and the muscles again admit of contracting on the application of a
stimulus.

t It should he stated here, however, that the generally accepted ex-
planation of the state of the muscles during rigor mortis, namely, that it
is due to contraction of the fibres, as instrong action during life, is denied
by some physiologists, who maintain that the condition of the muscles is
not due to contraction at all, but is caused by a kind of coagulation of
the inter-fibrillar juices. This idea has been of late especially sup-
ported by Dr. Norris (see Camb. J. of Anat. and Phys., Part I.).

Sal te ieee. 4 8. DB

Po > Se Pre
.

RIGOR MORTIS. | 593

The muscles are not affected exactly simultaneously by
the post-mortem contraction, but rather in succession. It
affects the neck and lower jaw first; next, the upper ex-
tremities, extending from above downwards; and lastly,
reaches the lower limbs; in some rare instances only, it
affects the lower extremities before, or simultaneously
with, the upper extremities, It usually ceases in the order |
in which it began; first at the head, then in the upper ex-
tremities, and lastly in the lower extremities. According
to Sommer, it never commences earlier than ten minutes,
and never later than seven hours, after death; and its
duration is greater in proportion to the lateness of its ~
accession. According to Schiffer, and others have con-
firmed the truth of his observation, heat is developed
during the passage of a muscular fibre into the condition

_of rigor mortis.

Since rigidity does not ensue until muscles have lost
the capacity of being excited by external stimuli, it follows

that all circumstances which cause a speedy exhaustion of

muscular irritability, induce an early occurrence of the
rigidity, white conditions by which the disappearance of
the irritability is delayed, are succeeded by a tardy onset
of this rigidity. Hence its speedy occurrence, and equally
speedy departure in the bodies of persons exhausted by
chronic diseases; and its tardy onset and long continuance
after sudden death from acute diseases. In some cases of
sudden death from lightning, violent injuries, or paroxysms
of passion, rigor mortis has been said not to occur at all;
but this is not alwaysthe case. It may, indeed, be doubted
whether there is really a complete absence of the post-
mortem rigidity in any such cases; for the experiments of

’ M. Brown-Séquard with electro-magnetism make it pro-

bable that the rigidity may supervene immediately after
death, and then pass away with such rapidity as to be
scarcely observable. Thus, he took five rabbits, and

killed them by removing their hearts. In the first, rigidity
QQ

504 MOTION.

came on in 10 hours, and lasted 192 hours; in the second,
which was feebly electrified, it commenced in seven hours,
and lasted 144; in the third, which was more strongly
electrified, it came on in two, and lasted 72 hours; in the
fourth, which was still more strongly electrified, it came
on in one hour, and lasted 20; while, in the last rabbit,
which was submitted to a powerful electro-galvanic cur-
rent, the rigidity ensued in seven minutes after death, and
passed away in 25 minutes. From this it appears that
the more powerful the electric current, the sooner does
the rigidity ensue, and the shorter is its duration; and as
the lightning shock is so much more powerful than any
ordinary electric discharge, the rigidity may ensue so early
after death and pass away so rapidly as to escape detection.
The influence exercised upon the onset and duration of
post-mortem rigidity by causes which exhaust the irritability
of the muscles, was well illustrated in further experiments
by the same physiologist, in which he found that the rigor
mortis ensued far more rapidly, and lasted for a shorter
period in those muscles which had been powerfully elec-
trified just before death than in those which had not been
thus acted upon. *

The occurrence of rigor mortis is not prevented by
the previous existence of paralysis in a part, provided the
paralysis has not been attended with very imperfect nutri-
tion of the muscular tissue.

The rigidity affects the involuntary as well as the volun-
tary muscles, whether they be constructed of striped or
unstriped fibres. The rigidity of involuntary muscles with
striped fibres is shown in the contraction of the heart
after death. The contraction of the muscles with un-
striped fibres is shown by an experiment of Valentin, who
found that if a graduated tube connected with a portion
of intestine taken from a recently-slain animal, be filled
with water, and tied at the opposite end, the water will in
a few hours, risé to a considerable height in the tube,

i il ie

RIGOR MORTIS. 595

owing to the contraction of the intestinal walls. It is still
better shown in the arteries, of which all that have mus-
‘cular coats contract after death, and thus present the
roundness and cord-like feel of the arteries of a limb lately
removed, or those of a body recently dead. Subsequently
they relax, as do all the other muscles, and feel lax and
flabby, and lie as if flattened, and with their walls nearly
in contact.*

Actions of the Voluntary Muscles.

The greater part of the voluntary muscles of the body
act as sources of power for moving levers,—the latter
consisting of the various bones to which the muscles are
attached.

All levers have been divided into three kinds, according

to the relative position of the power, the weight to be moved,

and the axis of motion or fulcrum. Ina lever of the /irst
kind the power is at. one extremity of the lever, the weight

- at the other, and the fulcrum between the two. If the

initial letters only of the power, weight, and fulcrum be
used, the arrangement will stand thus:—P.F.W. A

* Although the preceding remarks represent the views generally enter-
“tained in regard to muscular action, yet it must be observed that a new

:and very different theory on the subject has been lately advanced by
-several writers, and especially developed by Dr. Radcliffe, who has also

made it the basis of new views on the pathology of various convulsive

caffections. According to this doctrine, the ordinary relaxed or elongated

state of a muscle is due to a certain ‘‘ state of polarity ” in which the
muscle is maintained, and contraction is brought about by anything
(such as an effort of the will) which liberates the muscle from this

infiuence, and thus leaves it to the operation of the attractive force

inherent in the muscular molecules. According to this doctrine, also,
the stage of rigor mortis is readily explicable : death depriving the
muscles of the “ state of polarity” whereby they had hitherto been kept
relaxed, and thus allowing the attractive force of the muscular particles
to come into play. For facts and arguments in support of this view,
and for references and confirmatory opinions, Dr. Radcliffe’s work On
Epileptic and other Convulsive Affections may be consulted.
QQ2

596 MOTION.

poker, as ordinarily used, or the bar in fig. 164, may be
cited as an example of this variety of lever; while, as an
instance in which the bones of the human skeleton are
used as a lever of the same kind, may be mentioned the
act of raising the body from the stooping posture by
means of the hamstring muscles attached to the tuberosity
of the ischium (fig. 163).
Fig. 163.

P wPP w
i

'

'

i

bl|-----4

In a lever of the second kind, the arrangement is thus :

—P.W.F.; and this leverage is employed in the act of

raising the handles of a wheelbarrow, or in stretching

Fig. 164.
w

EvasticiiBano

[K{------=--44

ese

—.

an elastic band as in fig. 164. In the human body the-act
-of opening the mouth by depressing the lower jaw, is an
example of the same kind,—the tension of the muscles
which close the jaw representing the weight (fig. 164).

ee a

—— it atin ii

VARIETIES OF LEVERS. 597

In a lever of the third kind the arrangement is—F.P.W.,
and the act of raising a pole, as in fig. 165, is an-example.
In the human body there are numerous examples of the
employment of this kind of leverage. The act of bending
- the fore-arm may be mentioned as an instance (fig. 165).
Fig. 165.

w

i
'
!
1
:
i
!
i
I
|
!
!

|

In the human body, levers are most frequently used at a
disadvantage as regards power, the latter being sacrificed
for the sake of a greater range of motion. Thus in the
diagrams of the first and third kinds it is evident that the
_ power is so close to the fulcrum, that great force must be
exercised in order to produce motion. It is also evident,
however, from the same diagrams, that by the closeness of
the power to the fulcrum, a great range of movement can
be obtained by means of a comparatively slight shortening
of the muscular fibres.

The greater number of the more important muscular
actions of the human body—those, namely, which are
arranged harmoniously so as to subserve some definite
purpose or other in the animal economy—are described in
various parts of this work, in the sections which treat of
the physiology of the processes by which these muscular
actions are resisted or carried out. The combined action
of the respiratory muscles, for instance, will be found
described in the chapter on ‘“ Respiration’’; the action of
the heart and blood-vessels, under the head of ‘ Circula-
tion’’; while the movements of the stomach and intestines

598. MOTION.

are too intimately associated with the function of ‘‘ Diges-
tion,” to be described apart from it. There are, however,
one or two very important and somewhat complicated mus-
cular acts which may be best described in this place.

Walking.—In the act of walking, almost every voluntary ~

muscle in the body is brought into play, either directly
for purposes of progression, or indirectly for the proper
balancing of the head and trunk. The muscles of the:
arms are least concerned; but even these are for the most
part instinctively in action also to some extent. |

‘Among the chief muscles engaged directly in the act of
walking are those of the calf, which, by pulling up the
heel, pull up also the astragalus, and with it, of course,
the whole body, the weight of which is transmitted through
the tibia to this bone (fig. 166). When starting to walk,

Fig. 166.

say with the left leg, this raising of the body is not left:
entirely to the muscles of the left calf, but the trunk is
thrown forward in such a way that it would fall prostrate
were it not that the right foot is brought forward and
planted on the ground to support it. Thus the muscles.
of the left calf are assisted in their action by those muscles.
on the front of the trunk and legs which, by their con-
traction, pull the body forwards; and of course, if the
trunk form a slanting line, with the inclination forwards,
it is plain that when the heel is raised by the calf-muscles,
the whole body will be raised, and pushed obliquely for-
wards and upwards. The successive acts in taking the first
step in walking are represented in fig. 166, I, 2, 3.

af

hs

Lr ee

WALKING 599

Now it is evident that by the time the body has assumed
the position No. 3, it is time that the right leg should be
brought forward to support it and prevent it from falling
prostrate. This advance of the other leg (in this case the
right) is effected partly by its mechanically swinging for-
wards, pendulum-wise, and partly by muscular action ;
the muscles used being,—Ist, those on the front of the
thigh, which bend the thigh forwards on the pelvis, espe-
cially the rectus femoris, with the psoas and the iliacus ;
2ndly, the hamstring muscles, which slightly bend the leg
on the thigh; and 3rdly, the muscles on the front of the
leg, which raise the front of the foot and toes, and so pre-
vent the latter in swinging forwards from hitching in the
ground. Anybody who has attentively watched the help-
less flapping action of the foot and leg in cases of partial
paralysis affecting the muscles of the leg, or who will, in
his own case, note the act of bringing the leg forward in

_ walking, will be convinced of the large share which the

muscles take in the act in question; although, of course,
their work is rendered much easier by the pendulum-like
swinging forward of the leg by its own weight.

The second part of the act of walking, which has been
just described, is shown in the diagram (4, fig. 166).

When the right foot has reached the ground the action
of the left leg has not ceased. The calf-muscles of the
latter continue to act, and by pulling up the heel, throw
the body still more forwards over the right leg, now bearing
nearly the whole weight, until it is time that in its turn
the left leg should swing forwards, and the left foot be
planted on the ground to prevent the body from falling
prostrate. As at first, while the calf-muscles of one leg
and foot are preparing, so to speak, to push the body
forward and upward from behind by raising the heel, the
muscles on the front of the trunk and of the same leg (and
of the other leg, except when it is swinging forwards) are
helping the act by pulling the legs and trunk, so as to make

600 MOTION.

them incline forward, the rotation in the inclining forwards

being effected mainly at the ankle-joint. Two main kinds ©

of leverage are, therefore, employed in the act of walking,
and if this idea be firmly grasped, the detail will be under-
stood with comparative ease. One kind of leverage
employed in walking is essentially the same with that
employed in pulling forward the pole, as in fig. 165. And
the other, less exactly, is that employed in raising the
handles of a wheelbarrow. Now, supposing the lower end of
the pole to be placed in the barrow, we should have a very
rough and inelegant, but not altogether bad representation
of the two main levers employed in the act of walking.
The body is pulled forward by the muscles in front, much
in the same way that the pole might be by the force applied
at p, (fig. 165) while the raising of the heel and pushing

forwards of the trunk by the calf-muscles is roughly repre- —

sented on raising the handles of the barrow. The manner
in which these actions are performed alternately by each
leg, so that one after the other is swung forwards to sup-
port the trunk, which is at the same time pushed and pulled
forwards by the muscles of the other, may be gathered
from the previous description.

There is one more thing to be noticed especially in
the act of walking. Inasmuch as the body is being con-
stantly supported and balanced on each leg alternately, and
therefore on only one at the same moment, it is evident
that there must be some provision made for throwing the
centre of gravity over the line of support formed by the
bones of each leg, as, in its turn, it supports the weight
of the body. This may be done in various ways, and the
manner in which it is effected is one element in the dif-
ferences which exist in the walking of different people.
Thus it may be done by an instinctive slight rotation of
the pelvis on the head of each femur in turn, in such a
manner that the centre of gravity of the body shall fall
over the foot of this side. Thus when the body is pushed

So ic

Se LSS

— se

eee Te

—— ee ee ee

ae

in

WALKING. 601

onwards and upwards by the raising, say, of the right heel,
as in fig. 166, 3, the pelvis is instinctively, by various
muscles made to rotate on the head of the left femur at
the acetabulum, to Fig. 167.

the left side, so that tea aT r
the weight may fall
over the line of sup-
port formed by the
left leg at the time
that the right leg is
swinging forwards,
and leaving all the
work of support to
fall on its fellow.
Such a ‘rocking’
movement of the
trunk and pelvis,

however, is but an
awkward manner of
doing what can be
done more gracefully by combining a slight ‘rocking’ with
a movement of the whole trunk and leg over the foot which
is being planted on the ground (fig. 167) ; the action being
accompanied with a compensatory outward movement at
the hip, more easily appreciated by looking at the figure
(167) than described.

Thus the body in walking is continually rising and
swaying alternately from one side to the other, as its cen-
tre of gravity has to be brought alternately over one or
other leg; and the curvatures of the spine are altered in
correspondence with the varying position of the weight
which it has to support. The extent to which the body is
raised or swayed differs much in different people.

In walking, one foot or the other is always on the ground.
The act of leaping, or jumping, consists in so sudden a
raising of the heels by the sharp and strong contraction of

602 MOTION.

the calf-muscles, that the body is jerked off the ground.
At the same time the effect is much increased by first
bending the thighs on the pelvis, and the legs on the
thighs, and then suddenly straightening out the angles
thus formed. The share which this action has in pro-
ducing the effect may be easily known by attempting to
leap in the upright posture, with the legs quite straight.

Running is performed by a series of rapid low jumps
with each leg alternately ; so that, during each complete
muscular act concerned, there isa moment when both feet
are off the ground.

In all these cases, however, the description of the man-
ner in which any given effect is produced, can give but a
very imperfect idea of the infinite number of combined
and harmoniously arranged muscular contractions which
are necessary for even the simplest acts of locomotion.

Actions of the Involuntary Muscles.—The involuntary
muscles are for the most part not attached to bones
arranged to act as levers, but enter into the formation of
such hollow parts as require a diminution of their calibre
by muscular action, under particular circumstances. Ex-
amples of this action are to be found in the intestines,
urinary bladder, heart, and blood-vessels, gall-bladder,
gland-ducts, etc.

The difference in the manner of contraction of the striated
and non-striated fibres has been already referred to (p. 590);
and the peculiar vermicular or peristaltic action of the
latter fibres in some regions of the body has been described

"at p. 345.
Source of Muscular Action.

“It was formerly supposed that each act of contraction
on the part of a muscle was accompanied by a correlative
waste or destruction of its own substance; and that the
quantity of the nitrogenous excreta, especially of urea,
presumably the expression of this waste, was in exact pro-

SOURCE OF MUSCULAR ACTION. €03

portion to the amount of muscular work performed. It
has been found, however, both that the theory itself is
erroneous, and that the supposed facts on which it was
founded do not exist.

It is true that in the action of muscles, as of all other
parts, there is a certain destruction of tissue, or, in other
words, a certain ‘wear and tear,’ which may be repre-
sented by a slight increase in the quantity of urea excreted:
but it is not the correlative expression or only source
of the power manifested. The increase in the amount of
urea which is excreted after muscular exertion is by no
means so great as was formerly supposed; indeed, it is
very slight. And as there is no reason to believe that the
waste of muscle-substance can be expressed, with unim-
portant exceptions, in any other way than by an increased
excretion of urea, it is evident that we must look else-
where than in destruction of muscle, for the source of
muscular action. | For, it need scarcely be said, all force
manifested in the living body must be the correlative
expression of force previously latent in the food eaten or
the tissue formed; and'‘evidences of force expended in the
body must be found in the eaecreta. If, therefore, the
nitrogenous excreta, represented chiefly by urea, are not in
sufficient quantity to account for the work done, we must
look to the non-nitrogenous excreta as carbonic acid and
water, which, presumably, cannot be the expression of
wasted muscle-substance.

The quantity of these mnon-nitrogenous excreta is
undoubtedly increased by active muscular efforts, and ~
to a considerable extent; and whatever may be the
source of the water, the carbonic acid, at least, is the
result of chemical action in the system, and especially
of the combustion of non-nitrogenous food, although,
doubtless, of nitrogenous food also. We are, therefore,
driven to the conclusion,—that the substance of muscles
is not wasted in proportion to the work they perform; and

604 VOICE AND SPEECH, —

that the non-nitrogenous as well as the nitrogenous foods
may, in their combustion, afford the requisite conditions
for muscular action. The urgent necessity for nitrogenous
food, especially after exercise, is probably due more to
the need of nutrition by the exhausted muscles and other
tissues for which, of course, nitrogen is essential, than to
such food being superior to non-nitrogenous substances as a
source of muscular power. |

CHAPTER XVIII.
OF VOICE AND SPEECH.

In nearly all air-breathing vertebrate animals there are
arrangements for the production of sound, or voice, in some
part of the respiratory apparatus. In many animals the
sound admits of being variously modified and altered
during and after its production; and, in man, one of the
results of such modification is speech.

Mode of Production of the Human Voice.

It has been proved by observations on living subjects,
by means of the laryngoscope, as well as by experiments
on the larynx taken from the dead body, that the sound
of the human voice is the result of the inferior laryngeal
" ligaments, or true vocal cords (A, cv, fig. 172) which bound
the glottis, being thrown into vibration by currents of
expired air impelled over their edges. Thus, if a free open-
ing exists in the trachea, the sound of the voice ceases, but
returns on the opening being closed. An opening into the
air-passages above the glottis, on the contrary, does not
prevent the voice being formed. Injury of the laryngeal
nerves supplying the muscles which move the vocal cords

VOICE AND SPEECH. 605,

puts an end to the formation of vocal sounds; and when ~
these nerves are divided :

on both sides, the loss
of voice is complete.
Moreover, by forcing a
current of air through
the larynx in the dead
subject, clear vocal
sounds are produced,
thtough the epiglottis,
the upper ligaments of
the larynx or false vocal
cords, the ventricles be- a
tween them, and the in-
ferior ligaments or true
vocal cords, and the up-
per part of the aryte-
noid cartilages, be all —
removed; provided the
true vocal cords remain
entire, with their points
of attachment, and be
kept ‘tense and so ap-
proximated that the fis-
sure of the glottis may
be narrow.

-The vocal ligaments ©
or cord, therefore, may
be regarded as the pro-
per organs of the mere
voice : the modifications of the voice are effected by other

Fig. 168.*

' ™ Fig. 168. Outline showing the general form of the larynx, trachea,
and bronchi, as seen from before. 4.—h, the great cornu of the hyoid
bone ; ¢, epiglottis; ¢, superior, and /’, inferior cornu of the thyroid
cartilage ; ¢, middle of the cricoid cartilage ; ér, the trachea, showing
sixteen cartilaginous rings ; 6, the right, and 0’, the left bronchus.

606 VOICE AND SPEECH.

parts as well as by ©
them. Their struc-

ture is adapted to

enable them to vi-

brate like tense mem- |
branes, for they are

essentially composed

of elastic tissue; and

they are so attached

to the cartilaginous

parts of the larynx

that their position

and tension can be

variously altered by

the contraction of the

muscles which act on

these parts.

The Laryne.

The larynx, or or-
gan of voice, consists
essentially of two
elastic lips called the
vocal cords, which
are so attached to
certain cartilages
and so under the
control of certain
muscles, that they

3
‘s
rs
eS
ee
EF
A:
Z
z
a
=
9,
Zs
=
=
@:
x
=

|
a\ &
SS AF,

Ly ere

* Fig. 169. Outline showing the general form of the larynx, trachea,
and bronchias seen from behind. 4.—A, great cornu of the hyoid bone ;
t, superior, and ¢’, the inferior cornu of the thyroid cartilage : ¢, the
epiglottis ; a, points to the back of both the arytenoid cartilages, which
are surmounted by the cornicula ; c, the middle ridge on the back of the
cricoid cartilage; tr, the posterior membranous part of the trachea ;
b. b', right and left bronchi.

THE LARYNX. 607

can be made the means not only of closing the larynx
against the entrance and exit of air to or from the lungs,
but also can be stretched or relaxed, shortened or length-
ened, in accordance with the conditions that may be
necessary for the air in passing over them, to set them
vibrating and produce various sounds. ‘Their action in
respiration has been already referred to (p. 200), in con-—
nection with ordinary tranquil respiration, and also (p. 222,
et seq.) with other respiratory acts, in which the opening
or closing of the glottis, or, in other words, the close
apposition or separation of the vocal cords, is an essential
part of the performance. In these respiratory acts, how-
ever, any sound that may be produced, as in coughing,
is, so to speak, an accident, and not performed with

‘ purpose. In the present chapter the sound produced by

the vibration of the vocal cords is the only part of their
function with which we have to deal,

It will be well, perhaps, to refer to a few points in the
anatomy of the larynx, before considering its physiology in
connection with voice and speech.

The principal parts entering into the formation of the
larynx (figs. 169 and 170) are—(t) the thyroid cartilage ;
(c) the cricoid cartilage; (a) the two arytenoid cartilages ;
and the two true vocal cords (A, cv, fig. 172). The
epiglottis (fig. 170, e) has but little to do with the voice,
and is chiefly useful in falling down as a ‘lid’ over the
upper part of the larynx, to prevent the entrance of
food and drink in deglutition. The false vocal cords
(cvs, fig. 172), and the ventricle of the larynx, which is
a space between the false and the true cord of either side,
need be here only referred to.

The thyroid cartilage (fig. 170, I to 4) does not form a
complete ring around the larynx, but only covers the front
portion. The cricoid cartilage (fig. 170, 5, 6), on the other
hand, is a complete ring; the back part of the ring being
much broader than the front. On the top of this broad por-

608 VOICE AND SPEECH.

tion of the ¢ricoid are the arytenoid cartilages (fig. 169, a)
the connection between the cricoid below and arytenoid car-
tilages above being a joint with synovial membrane and liga-
ments, the latter permitting tolerably free motion between

Fig. 170.* them. But, although the aryte-
noid cartilages can move on the
cricoid, they of course accompany
the latter in all their movements,
just as the head may nod or
turn on the top of the spinal
column, but must accompany it
in all its movements as a whole.
. Thethyroid cartilage is also con-
nected with the cricoid, not only
by ligaments, but by two joints
with synovial membrane (¢’, figs.
168 and 169); the lowercornua of
the thyroid clasping, or nipping,
as it were, the cricoid between
them, but not so tightly but that
the thyroid can revolve, within a
certain range, around an axis passing transversely through
the two joints at which the ericoid is clasped. The vocal
cords are attached (behind) to the front portion of the base
of the arytenoid cartilages, and (in front) to the re-enter-
ing angle at the back part of the thyroid; it is evident,

therefore, that all movements of either of these cartilages

must produce an effect on them of some kind or other.
Inasmuch, too, as the arytenoid cartilages rest on the top
of the back portion of the cricoid cartilage (a, fig. 169),
and are connected with it by capsular and other ligaments,
all movements of the cricoid cartilage must move the

% Fig. 170. Cartilages of the larynx seen from before, 3.—1 to 4,
thyroid cartilage ; 1, vertical ridge or pomum Adami; 2, right ala ; 3,
superior, and 4, inferior cornu of the right side ; 5, 6, cricoid cartilage ;
5, inside of the posterior part ; 6, anterior narrow part of the ring; 7,
arytenoid cartilages.

SS ee ee ee ee

u

ee. eet "

THE LARYNX. — 609

arytenoid cartilages, and also produce an effect on the vocal
cords. 3
The so-called intrinsic muscles of the larynx, or those
which, in their action, have a direct action on the vocal
cords, are nine in number—four pairs, and a single
muscle; namely, two crico-thyroid muscles, two thyre-
arytenoid, two posterior crico-arytenoid, two lateral crico- |
arytenoid, and one arytenoid muscle. ‘Their actions are as
follows :—When the crico-thyroid muscles (10, fig. 171)
contract, they rotate the cricoid on the thyroid cartilage
in such a manner that the upper and back part of the
former, and of necessity the arytenoid cartilages on the
top of it, are tipped backwards, while the thyroid
is inclined forward: and
thus, of course, the vocal 2
cords being attached in j
front to one, and behind “nt j -
to the other, are ‘put on iti ill
the stretch.’ | LT i
The thyro-arytenoid mus- \\ a il /
‘les (7, fig...174), on the thi
fT
Po

Fig. 171.* '

other hand, have an
opposite action, —pulling
the thyroid backwards, and
the arytenoid and upper and
back part of the cricoid car-

tilages forwards, and thus
relaxing the vocal cords.

The crico-arytenoidei pos-
tictmuscles (fig. 17 3, b) dilate
the glottis, and separate the vocal cords, the one from
the other, by an action on the arytenoid cartilage, which
will be plain on reference.to w’ and c’, (fig. 172). By their

~ * Fig. 171. Lateral view of exterior of the larynx, after Mr. Willis.
8, Thyroid cartilage ; 9, Cricoid cartilage ; 10, Crico-thyroid muscle ;
11, Crico-thyroid Jigament ; 12, first rings of trachea.

RR

610 VOICE AND SPEECH.

contraction \they tend to pull together the outer angles
of the arytenoid cartilages in such a fashion as to rotate the
latter at their joint with the cricoid, and of course to throw
asunder their anterior angles to which the vocal cords are
attached.

These posterior crico-arytenoid muscles are opposed by
the crico-arytenoidei laterales, which, pulling in the opposite
direction from the other side of the axis of rotation, have
of course exactly the opposite effect, and close the glottis.
(fig. 174, 4 and 5).

The aperture of the glottis can be also contracted by
the arytenoid muscle (s, fig. 173, and 6, fig. 174), which,
in its contraction, pulls together the upper parts of the
arytenoid cartilages between which it extends.

The placing of the vocal cords in a position parallel
one with the other, is effected by a combined action of the
various little muscles which act on them—the thyro-aryte-
noidei having, without much. reason, the credit of taking
the largest share in the production of this effect. Fig. 172:
is intended to show the-various positions of the vocal cords.
under different circumstances. Thus, in ordinary tranquil
breathing, the opening of the glottis is wide and triangular,
becoming. a little wider at each inspiration, and a little
narrower at each expiration (fig. 172, see also p. 200). On
making a rapid and deep inspiration the opening of the
glottis is widely dilated, as in c, fig. 172, and somewhat.
lozenge-shaped. At the moment of the emission of sound,.
it is more narrowed, the margins of the arytenoid cartilages
being brought into contact, and the edges of the vocal
cords approximated and made parallel, at the same time
that their tension is much increased. The higher the note
produced, the tenser do the cords become (fig. 172, A); and
the range of a voice depends, of course, in the main, on the
extent to which the degree of tension of the vocal cords can
be thus altered. In the production of a high note, the
vocal cords are brought well within sight, so as to be

i ii

ACTIONS OF THE LARYNGEAL MUSCLES. OI!

plainly visible with the help of the laryngoscope. In the

utterance of grave tones, on the other hand, the epiglottis

is depressed and brought over them, and the arytenoid
Fig. 172.*

\
patter

Cc’

* Fig. 172. Thrée laryngoscopic views of the superior aperture of the
larynx and surrounding parts and different states of the glottis during
life (from Czermak).

A, the glottis during the emission of ‘a high note in singing ; B, in
easy and quiet inhalation of air; C,in the state of widest possible dila-
tation, as in inhaling a very deep breath. The diagrams A’, B’, and C’,
have been added to Czermak’s figures, to show in horizontal sections of
the glottis the position of the vocal ligaments and arytenoid cartilages
in the three several states represented in the other figures. In all the
figures, so far as marked, the letters indicate the parts as follows, viz. :
7, the base of the tongue ; ¢, the upper free part of the epiglottis ; é, the
tubercle or cushion of the epiglottis; ph, part of the anterior wall of
the pharynx behind the larynx ; in the margin of the aryteno-epiglot-
tidean fold w, the swelling of the membrane caused by the cartilages of

RR 2

612 | VOICE AND SPEECH.

cartilages look as if they were trying to hide themselves
under it (fig. 175).
The epiglottis, by being somewhat pressed down so as to
cover the superior cavity of the larynx, serves to render the
notes deeper in tone, and at
the same time somewhat
duller, just as covering the
end of a short tube placed

Fig. 173.*

tongues lowers the tone.
In no other respect does
the epiglottis appear to
have any effect in modify-
ing the vocal sounds.

The degree of approxi-
mation of the vocal cords
also usually corresponds
with the height of the
note produced; but pro-
bably not always, for the
width of the aperture has

no essential influence on
the height of the note, as
long as the vocal cords

Wrisberg ; s, that of the cartilages of Santorini; @, the tip or summit
of the arytenoid cartilages ; ¢ v, the true vocal cords or lips of the rima
glottidis ; ¢ vs, the superior or false vocal cords; between them the
ventricle of the larynx ; in C, ér is placed.on the anterior wall of the
receding trachea, and 0 indicates the commencement of the two bronchi
beyond the bifurcation which may be brought into view in this state of
extreme dilatation (from Quain’s Anatomy).

* Fig. 173. View of the larynx and part of the trachea from behind,
with the muscles dissected ; 2, the body of the hyoid bone ; e, epiglottis ;
t, the posterior borders of the thyroid cartilage ; c, the median ridge of
the cricoid ; a, upper part of the arytenoid ; s, placed on one of the
oblique fasciculi of the arytenoid muscle ; 6, left posterior crico-arytenoid
muscle; ends of the incomplete cartilaginous rings of the trachea;
1, fibrous membrane crossing the back of the trachea; 2, a
fibres exposed in a part (from Quain’s Anatomy).

in front of caoutchouc ,

=

-'.- ee oe

~ — SS em
ST =

of the aperture of the glottis,

duced by the passage of

PRODUCTION OF VOCAL SOUNDS.. 613

have the same tension; only with a wide aperture, the
tone is more difficult to produce, and is less perfect, the
rushing of the air through
the aperture being heard at
the same time.

No true vocal sound is pro-
duced at the posterior part

Fig. 174.*

that, viz., which is formed by
the space between the ary-
tenoid cartilages. For, as
Miiller’s experiments showed,
if the arytenoid cartilages
be approximated in such a
manner that their anterior processes touch each other, but
yet leave an opening behind them as well as in front, no
second vocal tone is pro- Fig. 175.+

the air through the pos-
terior opening, but merely
a rustling» or bubbling
sound; and the height or
pitch of the note produced
is the same whether the posterior part of the glottis be
open or not, provided the vocal cords maintain the same
degree of tension.

* Fig. 174. View of the anterior of larynx from above. 1, aperture
of glottis ; 2, arytenoid cartilages ; 3, vocal cords; 4, posterior crico-
arytenoid muscles; 5, lateral crico-arytenoid muscle of right side, that
of left side removed ; 6, arytenoid muscle ; 7, thyro-arytenoid muscle
of left side, that of right side removed ; 8, thyroid cartilage ; 9, cricoid
cartilage ; 13, posterior crico-arytenoid ligament. ~With the exception
of the arytenoid muscle, this diagram is a copy from Mr. Willis’s figure.

t Fig. 175. View of the upper partof the larynx as seen by means of
the laryngoscope during the utterance of a grave note. ¢, epiglottis ; s,
tubercles of the cartilages of Santorini; a, arytenoid cartilages ; z, base
of the tongue ; ph, the posterior wall of the pharynx.

614 VOICE AND SPEECH.

Application of the Voice in Singing and Speaking.

The notes of the voice thus produced may observe three
different kinds of sequence. The first is the monotonous,
in which the notes have nearly all the same pitch, as in
ordinary speaking; the variety of the sounds of speech
being due to articulation in the mouth. In speaking, how-
ever, occasional syllables generally receive a higher intona-
tion for the sake of accent. The second mode of sequence
is the successive transition from high to low notes, and vice
versa, without intervals; such as is heard in the sounds,
which, as expressions of passion, accompany crying in men,
and in the howling and whining of dogs. The third mode
of sequence of the vocal sounds is the musical, in which each
sound. has a determinate number of vibrations, and the
numbers of the vibrations in the successive sounds have
the same relative proportions that characterise the notes of
the musical scale.

The compass of the voice in different individuals, compre-
hends one, two, or three octaves. In singers—that is, in
persons apt for singing—it extends to two or three octaves.
But the male and female voices commence and end at dif-
ferent points of the musical scale. The lowest note of the
female voice is about an octave higher than the lowest of
the male voice; the highest note of the female voice about
an octave higher than the highest of the male. The com-
pass of the male and female voices taken together, or
the entire scale of the human voice, includes about four
octaves. The principal difference between the male and
female voice is, therefore, in their pitch; but they are
also distinguished by their tone,—the male voice is not so
soft.

The voice presents other varieties besides that of male
and female; there are two kinds of male voice, technically
called the bass and tenor, and two kinds of female voice,
the contralto and soprano, all differing from each other in

ONE a =

sae
2 ok” Sea

Se ee

COMPASS OF THE VOICE. 61k

tone, The bass voice usually reaches lower than the tenor
and its strength lies in the low notes; while the tenor voice
extends higher than the bass. The contralto voice has
generally lower notes than the soprano, and is strongest
in the lower notes of the female voice ; while the soprano
voice reaches higher in the scale. But the difference of
compass, and of power in different parts of the scale, is
not the essential distinction between the different voices ;
for bass singers can sometimes go very high, and the con-
tralto frequently sings the high notes like soprano singers.
The essentia. difference between the bass and tenor voices,
and between the contralto and soprano, consists in their

tone or “ timbre,”’ which distinguishes them even when

they are singing the same note. The qualities of the
barytone and mezzo-soprano voices are less marked; the
batytone being intermediate between the bass and tenor,
the mezzo-soprano between the contralto and soprano. They
have also a middle position as to pitch in the scale of the

male and female voices.

The different pitch of the male and the female voice
depends on tue different length of the vocal cords in the
two sexes; their relative length in men and women being
as three to two. The difference of the two voices in tone
or ‘‘timbre,’’ is owing to the different nature and form of
the resounding walls, which in the male laryux are much
more extensive, and form a more acute angle anteriorly.
The different qualities of the tenor and bass, and of the
alto and soprano voices, probably depend on some pecu-
liarities of the ligaments, and the membranous and car-
tilaginous parietes of the laryngeal cavity, which are —
not at present understood, but of which we may form some
idea, by recollecting that musical instruments made of dif-
ferent materials, e.g., metallic and gut-strings, may be tuned
to the same note, but that each will give it with a peculiar
tone or ‘‘ timbre.”

The larynx of boys resembles the female larynx; their

616 VOICE AND SPEECH.

vocal cords before puberty have not two-thirds the length
which they acquire at that period; and the angle of their
thyroid cartilage is as little prominent as in the female
larynx. Boys’ voices are alto and soprano, resembling in
pitch those of women, but louder, and differing somewhat
from them in tone. But, after the larynx has undergone
the change produced during the period of development at
puberty, the boy’s voice becomes bass or tenor. While
the change of form is taking place, the voice is said to
‘“crack;” it becomes imperfect, frequently hoarse and
crowing, and is unfitted for singing until the new tones
are brought under command by practice. In eunuchs,
who have been deprived of the testes before puberty, the
voice does not undergo this change. ‘The voice of most
old people is deficient in tone, unsteady, and more re-
stricted in extent: the first defect is owing to the ossifi-
cation of the cartilages of the larynx and the altered
condition of the vocal cord; the want of steadiness arises
from the loss of nervous power and command over the
muscles ; the result of which is here, as in other parts, a
tremulous motion. These two causes combined render the
voices of old people void of tone, unsteady, bleating, and
weak.

In any class of persons arranged, as in an orchestra,
according to the characters of voices, each would possess,
with the general characteristics of a bass, or tenor, or any
other kind of voice, some peculiar character by which his
voice would be recognized from all the rest. The con-
ditions that determine these distinctions are, however,
quite unknown. They are probably inherent in the
tissues of the larynx, and are as indiscernible as the
minute differences that characterize men’s features; one
often observes, in like manner, hereditary and family
peculiarities of voice as well marked as those of the limbs
or face.

Most persons, particularly men, have the power, if at all

ctl gp Me pe Ty Ae

OO

ET

VARIETIES OF LOCAL TONES. 617

capable of singing, of modulating their voices through a
double series of notes of different character: namely, the
notes of the natural voice, or chest-notes, and the falsetto
notes. The natural voice, which alone has been hitherto
considered, is fuller, and excites a distinct sensation of much
stronger vibration and resonance than the falsetto voice,
which has more a flute-like character. The deeper notes
of the male voice can be produced only with the natural
voice, the highest with the falsetto only ; the notes of middle
pitch can be produced either with the natural or falsetto
voice; the two registers of the voice are therefore not
limited in such a manner as that one ends when the other
begins, but they run in part side by side.

The natural, or chest-notes, are produced by the ordinary
vibrations of the vocal cords. The mode of production of
the falsetto notes is still obscure. By Miller they are
thought to be due to vibrations of only the inner borders
of the vocal cords. In the opinion of Petrequin and
Diday, they do not result from vibrations of the vocal cords
at all, but from vibrations of the air passing through the
aperture of tne glottis, which they believe assumes, at
such times, the contour of the embouchure of aflute. Others
(considering some degree of similarity which exists between
the falsetto notes, and the peculiar tones called harmonic,
which are produced when, by touching or stopping a harp-
string at a particular point, only a portion of its length is
allowed to vibrate) have supposed that, in the falsetto notes,
portions of the vocal ligaments are thus isolated, and
made to vibrate while the rest are held still. The question
cannot yet be settled; but any one in the habit of singing
may assure himself, both by the difficulty of passing
smoothly from one set of notes to the other, and by the
necessity of exercising himself in both registers, lest he
should become very deficient in one, that there must be
some great difference in the modes in which their respective
notes are produced. .

618. VOICE AND SPEECH.

The strength of the voice depends partly on the degree
to which the vocal cords can be made to vibrate; and
partly on the fitness for resonance of the membranes
and cartilages of the larynx, of the parieties of the thorax,
lungs, and cavities of the mouth, nostrils, and communi-
cating sinuses. It is diminished by anything which
interferes with such capability of vibration. The intensity
or loudness of a given note with maintenance of the same
“pitch,” cannot be rendered greater by merely increasing
the force of the current of air through the glottis; for
increase of the force of the current of air, cateris paribus,
raises the pitch both of the natural and the falsetto notes.
Yet, since a singer possesses the power of increasing the
loudness of a note from the faintest ‘‘ piano” to “‘ fortis-
simo”’ without its pitch being altered, there must be some
means of compensating the tendency of the vocal cords
to emit a higher note when the force of the current of air
is increased. This means evidently consists in modifying
the tension of the vocal cords. When a note is rendered
louder and more intense, the vocal cords must be relaxed
by remission of the muscular action, in proportion as the
force of the current of the breath through the glottis is
increased. When a note is rendered fainter, the reverse of
this must occur.

The arches of the palate and the uvula become contracted
during the formation of the higher notes; but their con-
traction is the same for a note of given height, whether it
be falsetto or not; and in either case the arches of the
palate may be touched with the finger, without the note
being altered. Their action, therefore, in the production
of the higher notes seems to be merely the result of involun-
tary associate nervous action, excited by the voluntarily
increased exertion of the muscles of the larynx. If the pala-
tine arches contribute at all to the production of the higher
notes of the natural voice and the falsetto, it can only be by
their increased tension strengthening the resonance. _

en

VARIETIES OF VOCAL TONES. 619

The office of the ventricles of the larynx is evidently to
afford a free space for the vibrations of the lips of the
glottis; they may be compared with the cavity at the
commencement of the mouth-piece of trumpets, which
allows the free vibration of the lips. |

SPEECH.

Besides the musical tones formed in the larynx, a great
number of other sounds can be produced in the vocal tubes,
between the glottis and the external apertures of the air-
passages, the combination of which sounds into different
groups to designate objects, properties, actions, etc., con-
stitutes language. The languages do not employ all the
sounds which can be produced in this manner, the com-
bination of some with others being often difficult. Those
sounds which are easy of combination enter, for the most
part, into the formation of the greater number of lan-
guages. Each language contains a certain number of
such sounds, but in no one are all brought together. On
the contrary, different languages are characterised by the
prevalence in taem of certain classes of these sounds, while
others are less frequent or altogether absent.

The sounds produced in speech, or articulate sounds, are
commonly divided into vowels and consonants ; the distinc-
tion between which is, that the sounds for the former are
generated by the larynx, while those for the latter are pro-
duced by interruption of the current of air in some part of
the air-passages above the larynx. The term consonant
has been given to these because several of them are not
properly sounded, except consonantly with a vowel. ‘Thus,
if it be attempted to pronounce aloud the consonants ), d,
and g, or their modifications, p, t, k, the intonation only
follows them in their combination with a vowel.

To recognize the essential properties of the articulate
sounds, we must, according to Miiller, first examine them
as they are produced in whispering, and then investigate

,

620 VOICE AND SPEECH.

which of them can also be uttered in a modified character
conjoined with vocal tone. By this procedure we find two
series of sounds: in one the sounds are mute, and cannot
be uttered with a vocal tone; the sounds of the other series
can be formed independently of voice, but are also capable
of being uttered in conjunction with it.

All the vowels can be expressed in a whisper without
vocal tone, that is, mutely. These mute vowel-sounds
differ, however, in some measure, as to their mode of
production, from the consonants. All the mute consonants
are formed in the vocal-tube above the glottis, or in the
cavity of the mouth or nose, by the mere rushing of the
air between the surfaces differently modified in disposition.
But the sound of the vowels, even when mute, has its
source in the glottis, though its vocal cords are not thrown
into the vibrations necessary for the production of voice ;
and the sound seems to be produced by the passage of the
current of air between the relaxed vocal cords. The same
vowel sound can be produced in the larynx when the mouth
is closed, the nostrils being open, and the utterance of all
vocal tone avoided. This sound, when the mouth is -open,
is so modified by varied forms of the oral cavity, as to
assume the characters of the vowels a, i, 0, u, in all their
modifications.

The cavity of the mouth assumes the same form for the
articulation of each of the mute vowels as for the cor-
responding vowel when vocalized; the only difference in
the two cases lies in the kind of sound emitted by
the larynx. Krantzenstein and Kempelen have pointed
out that the conditions necéssary for changing one and the
same sound into the different vowels, are differences in
the size of two parts—the oral canal and the oral opening ;
and the same is the case with regard to the mute vowels.
By oral canal, Kempelen means here the space between
the tongue and palate: for the pronunciation of certain
vowels both the opening of the mouth and the space just

SPEECH, . 621°

~mentioned are widened; for the pronunciation of other
vowels both are contracted; and for others one is wide,
the other contracted. Admitting five degrees of size, both
of the opening of the mouth and of the space between the
tongue and palate, Kempelen thus states the dimensions
of these parts for the following vowel sounds :—

}

Vowel. Sound. Size of oral opening. Size of oral canal.
a asin “far” 5 3
Gy <5 “name”’ 4 2
Crass “theme” 3 I
0 “go” 2 4
00 45 * cool ” I 5

Another important distinction in articulate sounds is,
that the utterance of some is only of momentary duration,
taking place during a sudden change in the conformation
of the mouth, and being incapable of prolongation by a
continued expiration. To this class belong}, p, d, and the
hard g. In the utterance of other consonants the sounds
may be continuous ; they may be prolonged, ad libitum, as
long as a particular disposition of the mouth and a constant
expiration are maintained. Among these consonants are
h, m,n, f, 8,7, 1. Corresponding differences in respect to
the time that may be occupied in their utterance exist in
the vowel-sounds, and principally constitute the differences
of long and short syllables. Thus, the a as in “ far” and
‘< fate,” the o as in ‘‘go” and “ fort,” may be indefinitely
prolonged ; but the same vowels (or more properly different
vowels expressed by the same letters), as in “can” and
‘“‘ fact,” in “‘ dog” and “ rotten,” cannot be prolonged.

All sounds of the first or explosive kind are insusceptible
of combination with vocal tone (‘‘intonation”’ ), and are
absolutely mute; nearly all the consonants of the second
or continuous kind may be attended with ‘ intonation.”

The peculiarity of speaking, to which the term ven-
triloquism is applied, appears to consist merely in the

622 VOICE AND SPEECH.

varied modification of the sounds produced in the larynx,
in imitation of the modifications which voice ordinarily
suffers from distance, etc. From the observations of
Miller and Colombat, it seems that the essential mechanical
parts of the process of ventriloquism consist in taking a
full inspiration, then keeping the muscles of the chest and
neck fixed, and speaking with the mouth almost closed,
and the lips and lower jaw as motionless as possible, while
air is very slowly expired through a very narrow glottis;
care being taken also, that none of the expired air passes
through the nose. But, as observed by Miller, much of
the ventriloquist’s skill in imitating the voices coming from
particular directions, consists in deceiving other senses than
hearing. We never distinguish very readily the direction
in which sounds reach our ear; and, when our attention
is directed to a particuliar point, our imagination is very
apt to refer to that point whatever sounds we may hear.

The tongue, which is usually credited with the power
of speech,—language and speech being often employed as
synonymous terms—plays only a subordinate, although
very important part. This is well shown by cases in which
nearly the whole organ has been removed on account of
disease. Patients who recover from this operation talk
imperfectly, and their voice is considerably modified; but
the loss of speech is confined to those letters, in the pro-
nunciation of which the tongue is concerned.

CHAPTER XIX.

THE SENSES.
SENSATION consists in the mind receiving, through the

medium of the nervous system, and, usually as the result
of the action of an external cause, a knowledge of certain

.
:
}

THE SENSES. — 623

qualities or conditions, not of external bodies but of the
nerves of sense themselves; and these qualities of the
nerves of sense are in all different, the nerve of each sense
having its own peculiar quality.

There are two principal kinds of sensation, named
common and special. The first is the consequence of the
ordinary sensibilty or feeling possessed by most parts of
the body, and is manifested when a part is touched, or in
any ordinary manner is stimulated. According to the
stimulus, the mind perceives a sensation of heat, or cold,
of pain, of the contact of hard, soft, smooth, or rough

objects, etc. From this, also, in morbid states, the mind

perceives itching, tingling, burning, aching, and the like
sensations. In its greatest perfection, common sensibility
constitutes touch or tact. Touch is, indeed, usually classed
with the special senses, and will be considered in the same:
group with them; yet it differs from them in being a pro-
perty common to many nerves, ¢.g., all the sensitive spinal
nerves, the pneumogastric, glosso-pharyngeal, and fifth
cerebral nerves, and in its impressions being communicable
through many organs.

Including the sense of touch, the special senses are five
in number,—the senses of sight, hearing, smell, taste,
and touch. The manifestation of each of the first three
depends on the existence of a special nerve; the optic for
the sense of sight, the auditory for that of hearing, and
the olfactory for that of smell. The sense of taste appears
to be a property common to branches of the fifth and of oP
glosso-pharyngeal nerves,

The senses, by virtue of the peculiar properties of their
several nerves, make us acquainted with the states of our
own body; and thus indirectly inform us of such qualities
and changes of external matter as can give rise to changes
in the condition of the nerves. That which through the
medium of our senses is actually perceived by the mind is,
indeed, merely a property or change of condition of our

ors ya THE SENSES,

nerves; but the mind is accustomed to interpret these
modifications in the state of the nerves produced by external

influences as properties of the external bodies themselves. _

This mode of regarding sensations is so habitual in the case
of the senses which are more rarely affected by internal
causes, that it is only on reflection that we perceive it to be
erroneous. In the case of the sense of feeling, on the con-
trary, where many of the peculiar sensations of the nerves
perceived by the sensorium are excited as frequently by
internal as by external causes, we more readily apprehend
the truth. For it is easily conceived that the feeling of
pain or pleasure, for example, is due to a condition of the
nerves, and is not a property of the things which excite it.
What is true of these is true of all other sensations; the
mind perceives conditions of the optic, olfactory, and other
nerves specifically different from that of their state of rest ;
these conditions may be excited by the contact of external
objects, but they may also be the consequence of internal
changes: in the former case the mind, having knowledge
of the object through either instinct or instruction, re-
cognizes it by the appropriate changes which it produces
in the state of the nerves. .

The special susceptibility of the different nerves of sense
for certain influences,—as of the optic nerve, or rather its
centre, for light; of the auditory nerve, or centre, for
vibrations of the air, etc., and so on,—is not due entirely
to those nerves having each a specific irritability for such
influences exclusively. For although, in the ordinary
events of life, the optic nerve is excited only by the undu-
lations or emanations of which light may consist, the audi-
tory only by vibrations of the air, and the olfactory only by
odorous particles—yet each of these nerves may have its
peculiar properties called forth by other conditions. In
fact, in whatever way and to whatever degree a nerve of
special sense is stimulated, the sensation produced is
essentially of the same kind; irritation of the optic nerve

a
— ee

—— ee a a ee ae

aay

THE SENSES, 625

invariably producing a sensation of light, of the auditory
nerve a sensation of some modification of sound. The
phenomenon must, therefore, be ascribed to a peculiar
quality belonging to each nerve of special sense. It has
been supposed, indeed, that irritation of a nerve of special
sense, when excessive, may produce pain; but experiments
seem to have proved that none of these nerves possess the
faculty of common sensibility. Thus Magendie observed
that when the olfactory nerves laid bare in a dog were
pricked, no signs of pain were manifested; and other ex-
periments of his seemed to show that both the retina and
optic nerve are insusceptible of pain.

External impressions on a nerve can give rise to no kind
of sensation which cannot also be produced by internal
causes, exciting changes in the condition of the same nerve.
In the case of the sense of touch, this is at once evident.
The sensations of the nerves of touch (or common sensi-
bility), excited by causes acting from without, are those of
cold and heat, pain and pleasure, and innumerable modifi-
cations of these, which have the same kind of sensation as
their element., All these sensations are constantly being
produced by internal causes, in all parts of our body en-
dowed with sensitive nerves. The sensations of the nerves
of touch are therefore states or qualities proper to them-
selves, and merely rendered manifest by exciting causes,
whether external or internal. The sensation of smell, also,
may be perceived independently of the application of any
odorous substance from without, through the influence
of some internal condition of the nerve of smell. The
sensations of the sense of vision, namely, colour, light, and
darkness, are also often perceived independently of all
external exciting causes. So, also, whenever the auditory
nerve is in a state of excitement, the sensations peculiar to
it, as the sounds of ringing, humming, etc., are perceived.

The same cause, whether internal or external, excites in

the different senses different sensations; in each sense the
8s

626 . THE SENSES.

sensations peculiar to it. For instance, one uniform internal
cause, which may act on all the nerves of the senses in the
same manner, is the accumulation of blood in their capil-
lary vessels, as in congestion and inflammation. This
one cause excites in the retina, while the eyes are closed,
the sensations of light and luminous flashes; in the audi-
tory nerve, the sensation of humming and ringing sounds;
in the olfactory nerve, the sense of odours; and in the
nerves of feeling, the sensation of pain. In the same way,
also, a narcotic substance introduced into the blood, excites
in the nerves of each sense peculiar symptoms; in the
optic nerves, the appearance of luminous sparks- before
the ‘eyes ; in the auditory nerves, “‘ tinnitus aurium”’ ; and
in the common sensitive nerves, the sensation of creeping
over the surface. So, also, among eaternal causes, the
stimulus ‘of electricity, or the mechanical influence of a
blow, concussion, or pressure, excites in the eye the sensa-
tion of light and colours; in the ear, a sense of a loud
sound or of ringing; in the tongue, a saline or acid taste ;
and at the other parts of the body, a perception of peculiar
jarring or of the mechanical impression, or a shock like it.

Although, in the cases just referred to, and in all ordi-
nary conditions, sensations are derived from peculiar con-
ditions of the nerves of sense, whether excited by external
or by internal causes, yet the mind may have the same
sensations independently of changes in the conditions of at
least the peripheral portions of the several nerves, and
even independently of any connection with the external
organs of the senses. The causes of such sensations are
seated in the parts of the brain in which the several nerves
of sense terminate. Thus pressure on the brain has been
observed to cause the sensation of light: luminous spectra
may be excited by internal causes after complete amaurosis
of the retina: and Humboldt states, that, in a man who
had lost one eye, he produced by means of galvanism,
luminous appearances on the blind side. Many of the

THE SENSES. | 6a

various morbid sensations attending diseases of the brain,
the vision of spectra, and the like, are of the same kind.

_ Again, although the immediate objects of the perception
of our senses are merely particular states induced in the
nerves, and felt as sensations, yet, inasmuch as the nerves
of the senses are material bodies, and therefore participate
in the properties of matter generally, occupying space,
being susceptible of vibratory motion, and capable of being
variously changed chemically, as well as by the action of
heat and electricity, they make known to the mind, by
virtue of the different changes thus produced in them by ©
‘external causes, not merely their own condition, but also
‘some of the different properties and changes of condition
‘of external bodies; as, ¢.g., progressive and tremulous
motion, chemical change, etc. The information concerning
external nature thus obtained by the senses, varies in each
sense, having a relation to the peculiar qualities or energies
of the nerve.

The sensation of motion is, like motion itself, of two kinds,
—progressive and vibratory. ‘The faculty of the percep-
tion of progressive motion is possessed chiefly by the
senses of vision, touch, and taste. Thus an impression is
perceived travelling from one part of the retina to another,
and the movement of the image is interpreted by the
mind as the motion of the object. The same is the case
in the sense of touch; so also the movement of a sensation
of taste over the surface of the organ of taste, can be
recognized. The motion of tremors, or vibrations, is
perceived by several senses, but especially by those of
hearing and touch. For the sense of hearing, vibrations
constitute the ordinary stimulus, and so give rise to the
perception of sound. By the sense of touch, vibrations
are perceived as tremors, occasionally attended with the
general impression of tickling; for instance, when a
vibrating body, such as a tuning fork, is approximated to

a very sensible part of the surface, the eye can communi-

ss 2

628 THE SENSES.

cate to the mind the image of a vibrating body, and can
distinguish the vibrations when they are very slow; it may
be also that the vibrations are communicated to the optic
as to the auditory nerye in such a manner that it repeats
them, or receives their impulses.

We are made acquainted with chemical actions principally
by taste, smell, and touch, and by each of these senses in
the mode proper to it. Volatile bodies disturbing the
conditions of the nerves by a chemical action, exert the
greatest influence upon the organ of smell; and many
matters act on that sense which produce no impression
upon the organs of taste and touch,—for example, many
odorous substances, as the vapour of metals, such as lead,
and the vapour of many minerals. Some volatile sub-
stances, however, are perceived not only by the sense of
smell, but also by the senses of touch and taste, provided
they are of a nature adapted to disturb chemically the
condition of those organs, and in case of the organ of
taste, to be dissolved by the fluids covering it. Thus, the
vapours of horse-radish and mustard, and acrid suffo-
cating gases, act upon the conjunctiva and the mucous
membrane of the lungs, exciting through the common
sensitive nerves, merely modifications of common feeling ;
and at the same time they excite the sensations of smell
and of taste. -

Sensations are referred from their proper seat towards
the exterior; but this is owing, not to anything in the
nature of the nerves themselves, but to the accompanying
idea derived from experience. For in the perception of sen-
sations, there is a combined action both of the mind and of
the nerves of sense; and the mind by education or experi-
ence, has learned to refer the impressions it receives to
objects external to the body. Even when it derives impres-
sions from internal causes, it commonly refers them to ex-
ternal objects. The light perceived in congestion of the
retina seems external to the body: the ringing of the ears

ae al ey

/ THE SENSES. 629

in disease is felt as if the sound came from some distance: —
the mind referring it to the outer world from which itis in
the habit of receiving the like impression.

Moreover, the mind not only perceives the sensations,

_ and interprets them according to ideas previously obtained,

but it has a direct influence upon them, imparting to them
intensity by its faculty of attention. Without simultaneous
attention, all sensations are only obscurely, if at all, per-
ceived.,. If the mind be torpid in indolence, or if the
attention be withdrawn from the nerves of sense in in-
tellectual contemplation, deep speculations, or an intense
passion, the sensations of the nerves make no impres-
sion upon the mind; they are not perceived,—that is to
say, they are not communicated to the conscious “self,” or
with so little intensity, that the mind is unable to retain the
impression, or only recollects it some time after, when it is
freed from the preponderating influence of the idea which
had occupied it.

This power of attention to the sensations derived from a
single organ, may also be exercised in a single portion of
a sentient organ, and thus enable one to discern the detail
of what would otherwise be a single sensation. For
example, by well-directed attention, one can distinguish
each of the many tones simultaneously emitted by an
orchestra, and can even-follow the weaker tones of one in-
strument apart from the other sounds, of which the impres-
sions being not attended to are less vividly perceived. So,
also, if one endeavours to direct attention to the whole field
of vision at the same time, nothing is seen distinctly; but
when the attention is directed first to this, then to that part,
and analyses the detail of the sensation, the part to which
the mind is directed is perceived with more distinctness than
the rest of the same sensation.

630 THE SENSES...
THE SENSE OF SMELL.

The sense of smell ordinarily requires, for its excitement
to a state of activity, the action of external matters, which.
action produces certain changes in the olfactory nerve; and
this nerve is susceptible of an infinite variety of states de-
pendent on the nature of the external stimulus..

The first condition essential to the sense of smell is the
existence of a special nerve, the changes in whose condition
are perceived as sensations of odour; for no other nerve is
capable of these sensations, even though acted on. by the
same causes. The same substance which excites the sen-
sation of smell in the olfactory nerves may cause another
peculiar sensation through the nerves of taste, and may pro-
duce an irritating and burning sensation on the nerves of
touch ; but the sensation of odour is yet separate and distinct
from these, though it may be simultaneously perceived.
The second condition of smell is a peculiar state of the
olfactory nerve, or a peculiar change produced in it by
the stimulus or odorous substance.

The material causes of odours are, usually, in the case of
animals living in the air, either solids suspended ina state
of extremely fine division in the atmosphere; or gaseous
exhalations often of so subtle a nature that they can be
detected by no other re-agent than the sense of smell itself.
The matters of odour must, in all cases, be dissolved in the
mucus of the mucous membrane before they can be imme-
diately applied to, or affect the olfactory nerves; therefore
a further condition necessary for the perception of odours is,
that the mucous membrane of the nasal cavity be moist.
When the Schneiderian membrane is dry, the sense of smell.
is impaired or lost; in the first stage of catarrh, when
the secretion of mucus within the nostrils is lessened, the.
faculty of perceiving odour is either lost, or rendered very
imperfect.

In animals living in the air, it is also requisite that the-

Lei ey Hes

THE SENSE OF SMELL. 631

odorous matter should be transmitted in a current through
the nostrils. This is effected by an inspiratory movement,
the mouth being closed; hence we have voluntary influence
over the sense of smell; for by interrupting respiration
we prevent the perception of odours, and by repeated quick
inspiration, assisted, as in the act of sniffing, by the action
of the nostrils, we render the impression more intense (see
p. 224).

The human organ of smell is essentially formed by the
filaments of the olfactory nerves, distributed in minute

Fig. 176.*

arrangement, in the mucous membrane covering the upper
third of the septum of the nose, the superior turbinated or
spongy bone, the upper part of the middle turbinated bone
and the upper wall of the nasal cavities beneath the cribri-
form plates of the ethmoid bones (figs. 176 and 177).
This olfactory region is covered by cells of cylindrical epi-

* Fig. 176. Nerves of the septum nasi, seen from the right side (from
Sappey after Hirschfeld and Leveillé). 3.—I, the olfactory bulb ;
1, the olfactory, nerves passing through the foramina of the cribriform
plate, and descending to be distributed on the septum ; 2, the internal
or septal twig of the nasal branch of the ophthalmic nerve ; 3, naso-
palatine nerves.

632; . THE SENSE OF SMELL.

thelium not provided with cilia; and interspersed with these
are peculiar fusiform cells with fine processes, called olfactory
cells. They are supposed to have some connection with the
Fig. 177." terminal filaments of
the olfactorynerve. The
lower, or respiratory
part, as it is called, of
the nasal fossee is lined
by cylindrical ciliated
epithelium, except -in
the region of the nos-
trils, where it is squa-
m2L0US.

In all the distribu-
tion, the branches of
the olfactory nerves re-
tain much of the same
soft and greyish tex-
ture which distinguishes
their trunks (as the olfactory lobes of the brain are called)
within the cranium. ‘There individual filaments, also, are
peculiar, more resembling those of the sympathetic nerve
than the filaments of the other cerebral nerves do, con-
taining no outer white substance, and being finely granular
and nucleated. The branches are distributed principally
in close plexuses; but the mode of termination of the fila-
ments is not yet satisfactorily determined.

* Fig. 177. Nerves ofthe outer walls of the nasal fosse (from Sappey
after Hirschfeld and Leveillé). 2.—1, network of the branches of the
olfactory nerve, descending upon the region of the superior and middle
turbinated bones; 2, external twig of the ethmoidal branch of the
nasal nerves ; 3, spheno-palatine ganglion ; 4, ramification of the anterior
palatine nerves ; 5, posterior, and 6, middle divisions of the palatine
nerves ; 7, branch to the region of the inferior turbinated bone; 8,
branch to the region of the superior and middle turbinated bones ; 9,
naso-palatine branch to the septum cut short (after Sharpey).

THE SENSE OF SMELL. 633

The sense of smell is derived exclusively through those
parts of the nasal cavities in which the olfactory nerves
are distributed; the accessory cavities or sinuses com-
municating with the nostrils seem to have no relation to it.
Air impregnated with the vapour of camphor was injected
by Deschamps into the frontal sinus through a fistulous
opening, and Richerand injected odorous substances into
the antrum of Highmore; but in neither case was any
odour perceived by the patient. The purposes of these
sinuses appear to be, that the bones, necessarily large for
the action of the muscles and other parts connected with
them, may be as light as possible, and that there may be
more room for the resonance of the air in vocalising. The
former purpose, which is in other bones obtained by filling
their cavities with fat, is here attained, as it is in many
bones of birds, by their being filled with air.

All parts of the nasal cavities, whether or not they can
be the seats of the sense of smell, are endowed with com-
mon sensibility by the nasal branches of the first and
second divisions of the fifth nerve. Hence the sensations
of cold, heat, itching, tickling, and pain; and the sensa-
tion of tension or pressure in the nostrils. That these
nerves cannot perform the function of the olfactory nerves
is proved by cases in which the sense of smell is lost, while
the mucous membrane of the nose remains susceptible of
the various modifications of common sensation or touch.
But it is often difficult to distinguish the sensation of smell
from that of mere feeling, and to ascertain what belongs
to each separately. This is the case particularly with the
sensations excited in the nose by acrid vapours, as of am-
monia, horse-radish, mustard, etc., which resemble much
the sensations of the nerves of touch; and the difficulty is
the greater, when it is remembered that these acrid vapours
have nearly the same action upon the mucous membrane
of the eyelids. It was because the common sensibility of
the nose to these irritating substances remained after the

634 THE SENSE OF SMELL. |

destruction of the olfactory nerves, that Magendie was led
to believe the fifth nerve might exercise the special sense.
Animals do not all equally perceive the same odours;
the odours most plainly perceived by an herbivorous animal
and by a carnivorous animal are different. The Carnivora
have the power of detecting most accurately by the smell
the special peculiarities of animal matters, and of track-
ing other animals by the scent; but have apparently very
little sensibility to the odours of plants and flowers.
Herbivorots animals are peculiarly sensitive to the latter,
and have a narrower sensibility to animal odours, especially
to such as proceed from other individuals than their own

species. Man is far inferior to many animals of both |

classes in respect of the acuteness of smell; but his sphere
of susceptibility to various odours is more uniform and
extended. The cause of this difference lies probably in
the endowments of the cerebral parts of the olfactory
apparatus.

Opposed to the sensation of an agreeable odour is that
of a disagreeable or disgusting odour, which corresponds
to the sensations of pain, dazzling and disharmony of
colours, and dissonance in the other senses. The cause
of this difference in the effect of different odours is un-
known; but this much is certain, that odours are pleasant
or offensive in a relative sense only, for many animals
pass their existence in the midst of odours which to us are
highly disagreeable. A great difference in this respect is,
indeed, observed amongst men: many odours, generally
thought agreeable, are to some persons intolerable; and
different persons describe differently the sensations that
' they severally derive from the same odorous substances.
There seems also to be in some persons an insensibility to
certain odours, comparable with that of the eye to certain
colours; and among different persons, as great a difference
in the acuteness of the sense of smell as among others in
the acuteness of sight. We have no exact proof that a

ee

Set he

7

THE SENSE OF SMELL. 635

relation of harmony and disharmony exists between odours
as between colours and sounds; though it is probable that
such is the case, since it certainly is so with regard to the
sense of taste; and since such a relation would account
in some measure for the different degrees of perceptive
power in different persons; for as some have no ear for
music (as it is said), so others have no clear appreciation
of the relation of odours, and therefore little pleasure in
them.

The sensations of the olfactory nerves, independent of
the external application of odorous substances, have
hitherto been little studied. It has been found that
solutions of inodorous substances, such as salts, excite no
sensation of odour when injected into the nostrils. The
friction of the electric machine is, however, known to
produce a smell like that of phosphorus. Ritter, too, has
observed, that when galvanism is applied to the organ of
smell, besides the impulse to sneeze, and the tickling
sensation excited in the filaments of the fifth nerve, a
smell like that of ammonia was excited by the negative
‘pole, and an acid odour by the positive pole; whichever of
these sensations was produced, it remained constant as long
as the circle was closed, and changed to the other at the
moment of the circle being opened. Frequently a person
smells something which is not present, and which other
persons cannot smell; this is very frequent with nervous
people, but it occasionally happens to every one. In
aman who was constantly conscious of a bad odour, the
_ arachnoid was found after death, by MM. Cullerier and
Maignault, to be beset with deposits of bone; and in the
middle of the cerebral hemispheres were scrofulous cysts
in a state of suppuration. Dubois was acquainted with a
man, who, ever after a fall from his horse, which occurred
several years before his death, believed that he smelt a bad
odour.

636 THE SENSE OF SIGHT.

THE SENSE OF SIGHT.

The eyeball or the organ of vision (fig. 178) consists of
a variety of structures which may be thus enumerated :—

Fig. 178.

Ciliary muscle-
Ciliary process—-
Canal of Petit-+&

Cornea-.

Se Weer
ee |

Lens-- Ee OL ALT ee

Anterior chamber-

The sclerotic, or outermost coat, envelops about five-
sixths of the eyeball: continuous with it, in front, and
occupying the remaining sixth, is the cornea. The cornea
and front portion of the sclerotic are covered by mucous
membrane,—the conjunctiva ; that which covers the front
of the cornea being little more than squamous epithelium.
immediately within the sclerotic is the choroid coat, and
within the choroid is the retina. The interior of the eye-
ball is well-nigh filled by the aqueous and vitreous humours
and the crystalline lens ; but also, there is suspended in the
interior a contractile and perforated curtain,—the iris, for
regulating the admission of light, and behind the junction
of the sclerotic and cornea is the ciliary muscle, the fune-
tion of which is to adapt the eye for seeing objects at
various distances,

‘

and behind the fibrous tissue of

consists of a thin and highly vascu-

THE SENSE OF SIGHT, 637

These structures may be now examined rather more in
detail. | .

The sclerotic coat is composed of connective tissue,
arranged in variously disposed and intercommunicating
layers. It is strong, tough, and opaque, and not very
elastic.

The cornea (fig. 179) is, like the sclerotic, with which it
is continuous, chiefly of a fibrous
structure, but the fibres are so
modified and arranged as to form
a transparent membrane for the
passage of light. Both in front of

the cornea is a structureless elastic
membrane with epithelium.

The choroid, which is the next
tunic of the eye within the sclerotic
and immediately outside the retina,

lar membrane, of which the inter-
nal surface is covered by a layer ~
of black pigment cells. The prin-
cipal use of the choroid is to absorb,
by means of its pigment, those rays
of light which pass through the
transparent retina, and thus to
prevent their being thrown again
upon the retina, so as to interfere

* Fig. 179. Structure of the cornea (after Bowman). A °,B&C, *?
A, Small portion of a vertical section of the cornea in the adult ; a, con-
junctival epithelium ; 3, anterior elastic lamina ; ¢ to d, fibrous laminz
with nuclear bodies interspersed between them; c, fibres shooting
through some of these layers from the, external elastic lamina; d, pos- —
terior elastic lamina or membrane of Demours ; ¢, internal epithelium
of d. B, epithelium of the membrane of Demours, as seen looking
towards its surface. C, the same seen in section,

638 THE SENSE OF SIGHT.

Fig. 180.* with the distinctness of.

Ny the images there formed.
Hence animals in which
the choroid is destitute of
pigment, and human Albi-
noes, are dazzled by day-
light and see best in the
twilight. The choroid coat
ends in front in what are
called the ciliary processes
(fig. 180).

The retina (fig. 181) is
a delicate membrane,
concave, with the conca-
vity directed forwards
and endingin front, near
the outer part of the
ciliary processes In a
finely notched edge,—
Vay ff, the ora serrata. Semi-
transparent when fresh,
it soon becomes clouded
and opaque, with a
pinkish tint from the
blood in its . minute

Poy Ly

* Fig. 180. Ciliary processes as seen from behind. ?.—1, posterior
surface of the iris, with the sphincter muscle of the pupil; 2, anterior
part of the choroid coat ; 3, one of the ciliary processes, of which about
seventy are represented.

t Fig. 181. The posterior half of the retina of the left eye viewed

from before (after Henle) ; s, the cut edge of the sclerotic coat ; ch, the ©

choroid ; 7, the retina ; in the interior at the middle, the macula lutea
with the depression of the fovea centralis is represented by a slight oval
shade ; towards the left side the light spot indicates the colliculus or
eminence at the entrance of the optic nerve, from the centre of which
the arteria centralis is seen spreading its branches into the retina,
leaving the part occupied by the macula comparatively free.

a ee eee oe

ain ae

"i seta

hk

i) .
*: GME

THE SENSE OF SIGHT. 639°

vessels, it results from the sudden spreading out or ex-
pansion of the optic nerve, of whose terminal fibres, appa-
rently deprived of their external white substance, together
with nerve-cells, it is essentially composed.

Exactly in the centre of the retina, and at a point thus
corresponding to the axis of the | Fig. 182.*
eye in which the sense of vision B
is most perfect, is a round yellow- .
ish elevated spot, about =, of
an inch in diameter, having a ,
minute aperture at its summit,
and called after its discoverer the
yellow spot of Semmering. It is
not covered by the fibrous part
of the retina, but a layer of
closely-set cells passes over it,
and in its centre is a minute j
depression called fovea centralis,
About - of an inch to the
inner side of the yellow spot, and
consequently of the axis of the
eye, is the point at which the
optic nerve spreads out its fibres
to form the retina. This is the

* Fig. 182. Vertical section of a small part of the retina (after Kélliker),
259. A, entire section of a small part of the retina; B, two cones re-
presented separately in their connection with the fibres of Miiller and
other structures ; C, two rods represented separately in their connection
with the granules, fibres of Miiller and the nerve-cells; 1, columnar
layer; @, in A and C, the rods, in B, the terminal part of the cone ; 3,
cones ; 2, granular layer; .c, outer layer of nuclei (striated corpuscles of
Henle) ; d@, inner layer of nuclei; jf, inter-nuclear layer; 3, nervous
layer; g, fine molecular substance outside h, the nerve-cells; %, nerve
fibres ; 7, membrana limitans; ¢, inner ends of the fibres of Miiller ’
resting on the limiting membrane.

640 ~ _ THE SENSE OF SIGHT.

only point of the surface of the retina from which the
‘power of vision is absent,

On making a vertical section of the retina, it is seen,
under the microscope, to be composed of several layers
which differ from each other in structure and arrangement,
while besides these there are fibres, the so-called jibres of
Miiller, which extend through the different layers, and
perforate them, so to speak. Fig. 182 represents a verti-
cal section of a small piece of the retina. On examina-
tion it-will be seen that there are three principal layers,
bounded on the inner aspect by a membrana limitans,
and on the outer by the choroid coat. 1. The outermost
is the membrane of Jacob, or the columnar layer. 2. In
the middle is the granular layer. 3. The innermost
is the nervous layer. Each of these layers, again, is com-
posed of different strata, after the fashion shown in the
figure.

The columnar layer (Jacob’s membrane) is composed of
cylindrical or staff-shaped, transparent and highly refrac-
tive bodies, arranged perpendicularly to the surface of the
retina, with their outer extremities imbedded, to a greater
or less depth, in a layer of black pigment of the choroid
coat. Recent researches seem to have determined that
this membrane, instead of being, as was formerly con-
sidered, an independent covering, is intimately associated,
both in structure and function, with the sensitive part of
the retina; for the conical and staff-shaped bodies, of
which it is composed, appear to be connected, by means of
delicate fibres issuing from them, with the nerve-vesicles
of the retina, and even to become continuous with the
radiating processes which some of these vesicles present.
Concerning the use of these bodies, the discovery of their
connection with the sensitive part of the retina supports
the opinion entertained by Kélliker and H. Miller, that
their special office is to receive and transmit impressions
of light.

STRUCTURE OF THE RETINA. 641

~The structures of which the granular layer is composed
are indicated in the figure. |

The nervous layer is composed of nerve-corpuscles and
nerve-fibres. The nerve-corpuscles are the outermost, and
are most numerous over the yellow spot, and absent alto-
gether from the point of entrance of the optic nerve.
They are imbedded in fine molecular matter, which also
forms a layer outside them. The nerve-/ibres radiate as a
fine membranous network from the point of entrance of
the optic nerve, of whose fibres they are the continuation.
They end probably in the nerve-corpuscles. The fibres are
absent from the yellow spot.

Two of the jibres of Miiller are, for the sake of illustra-
tion, arranged in the figure separately on each side of the
layer which they perforate. About the connection of the
fibres of Miiller there is some uncertainty. They are
supposed to be connected by their owter ends with the rods
and cones; and by their wmner, which are thought to be
modifications of connective tissue, they rest on the mem-
brana limitans. Between these points they are supposed
to have connections also with some of the other structures
through which they pass, especially with the inner layer
of nuclei.

The retinal blood-vessels ramify chiefly in the nervous
layer.

The structures which have been just described are modi-
fied in their distribution over the yellow spot in the follow-
ing manner :—Of the columnar layer, or membrana Jacobi,
the cones greatly predominate; of the nervous layers the
ceils are numerous, while the nerve-fibres are absent.
There are capillaries here, but none of the larger branches
of the retinal arteries. Opposite the fovea centralis, there
are, moreover, neither the granular, nor the fine molecular
layer, nor the fibres of Miiller.

By means of the retina and the other parts just described,

a provision is afforded for enabling the terminal fibres of
B a

642 - THE SENSE OF SIGHT.

the optic nerve to receive the impression of rays of light,
and to communicate them tothe brain, in which they excite
the sensation of vision. But that light should produce in
the retina images of the objects from which it comes, it is
necessary that, when emitted or reflected from determinate
parts of the external objects, it should stimulate only
corresponding parts of the retina. For as light radiates
from a luminous body in all directions, when the media
offer no impediment to its transmission, a luminous point
will necessarily illuminate all parts of a surface, such as
the retina opposed to it, and not merely one single point.
A retina, therefore, without any optical apparatus placed
in front of it to separate the light of different objects, would
see nothing distinctly, but would merely perceive the
general impression of daylight, and distinguish it from the
night. Accordingly, we find that in man, and all ver-
tebrate animals, certain transparent refracting media are
placed in front of the retina for the purpose of collecting
together into one point, the different divergent rays emitted
by each point of the external body, and of giving them such
directions that they shall fall on corresponding points of
the retina, and thus produce an exact image of the object
from which they proceed. These refracting media are, in
the order of succession from without inwards, the cornea,
the aqueous humour, the crystalline lens, and the vitreous
humour (fig. 178).

The cornea, the structure of which has been already
referred to (p. 637), is in a twofold manner capable of
refracting and causing convergence of the rays of light
that fall upon and traverse it. It thus affects them first,
by its density ; for it is a law in optics that when rays of
light pass from a rarer into a denser medium, if they im-

-| pinge upon the surface in a direction removed from the
| perpendicular, they are bent out of their former direction
towards that of a line perpendicular to the surface of the

‘denser medium; and, secondly, by its convexity ; for it is

Ds bet

cote 4.5

ied a) a
cae A ae

Es ee
‘

REFRACTION BY THE CORNEA. 643

another law in optics that rays of light impinging upon a
convex transparent surface, are ‘refracted towards the |
centre, those being most refracted which are farthest from

the centre of the convex surface.
Behind the cornea is a space containing a thin watery
fluid, the aqueous humour, holding in solution a small quan-

- tity of chloride of sodium and extractive matter. The

space containing the aqueous humour is divided into an
anterior and posterior chamber by a membranous partition,
the iris, to be presently again mentioned. The effect pro-
duced by the aqueous humour on the rays of light travers-
ing it, is not yet fully ascertained. Its chief use, probably,
is to assist in filling the eyeball, so as to maintain its proper
convexity, and at the same time to furnish a medium in
which the movements of the iris can take place.

Behind the aqueous humour and the iris, and imbedded
in the anterior part of the me-
dium next to be described, viz.,
the vitreous humour, is seated a
doubly-convex body, the crystal-
line lens, which is the most im-
portant refracting structure of
the eye. The structure of the
lensis very complex. Itconsists
essentially of fibres united side
by side to each other, and

arranged together in very numerous laminz, which are so |
placed upon one another, that when hardened in spirit

the lens splits into three portions, in the form of sectors,
each of which is composed of superimposed concentric

- laminee. The lens increases in density and, consequently,

in power of refraction, from without inwards; the central

* Fig. 183. Laminated structure of the crystalline lens (from Ar-
nold), 4.—The lamin are split up after hardening in alcohol. 1, the
denser central part or nucleus ; 2, the successive external layers,

TT 2

—

|

It
[Nees
|

A a -
X ‘UN

644 THE SENSE OF SIGHT.

part, usually termed the nucleus, being the most dense.
The density of the lens increases with age; it is com-
paratively soft in infancy, but very firm in advanced life :
it is also more spherical at an early period of life than in
old age.

The vitreous humour constitutes nearly four-fifths of the
whole globe of'the eye. It fills up the space between the
retina and the lens, and its soft jelly-like substance con-
sists essentially of numerous layers, formed of delicate,
simple membrane, the spaces between which are filled with
a watery, pellucid fluid. It probably exercises some share
in refracting the rays of light to the retina; but its princi-
pal use appears to be that of giving the proper distension
to the globe of the eye, and of keeping the surface of the

- retina at a proper distance from the lens.

As already observed, the space occupied by the aqueous
humour is divided into two portions by a vertically-placed
membranous diaphragm, termed the iris, provided with
a central aperture, the pupil, for the transmission of light.

| The iris is composed of organic muscular fibres imbedded
| in ordinary fibro-cellular or connective tissue. The mus-
cular fibres of the iris have a direction, for the most part, -

radiating from the circumference towards the pupil; but
as they approach the pupillary margin, they assume a
circular direction, and at the very edge form a complete
ring. By the contraction of the radiating fibres, the size

of the pupil is enlarged: by the contraction of the circular —

ones, which resemble a kind of sphincter, it is diminished.

The object effected by the movements of the iris, is the —

regulation of the quantity of light transmitted to the
retina; the quantity of which is, ceteris paribus, directly
proportioned to the size of the pupillary aperture. The
posterior surface of the iris is coated with a layer of dark

' pigment, so that no rays of light can pass to the retina,

except such as are admitted through the aperTaey of the
pupil,

A~feo late fe ee

>

THE VITREOUS HUMOUR AND IRIS, 645

The ciliary muscle is composed of organic muscular fibres,
which form a narrow zone around the interior of the eye-
ball, near the line of junction of the cornea with the
sclerotic, and just behind the outer border of the iris (fig.
178). The outermost fibres of this muscle are attached in
front to the inner part of the sclerotic and cornea at their
line of junction, and, diverging somewhat, are fixed to the
ciliary processes, and a small portion of the choroid imme-
diately behind them. The inner fibres, immediately within
the preceding, form a circular zone around the interior of
the eye-ball, outside the ciliary processes. They compose
the ring formerly called the ciliary ligament.

The function of this muscle is to adapt the eye for
seeing objects at various distances. The manner in
which it effects this object will be considered afterwards
(p. 650).

The contents of the ball of the eye are surrounded and
kept in position by the cornea, and the dense, fibrous mem-
brane before referred, to as the sclerotic, which, besides thus
encasing the contents of the eye, serves to give attach-
ment to the. various muscles by which the movements
of the eye-ball are effected. These muscles, and the
nerves supplying them, have been already considered

(p. 539, et seq.)

Of the Phenomena of Vision.

The essential constituents of the optical apparatus of the
eye may be thus enumerated :—a nervous structure to
receive and transmit to the brain the impressions of light;
certain refracting media for the purpose of so disposing of
the rays of light traversing them as to throw a correct
image of an external body on the retina; a contractile
diaphragm with a central aperture for regulating the
quantity of light admitted into the eye; and a contractile
structure by which the chief refracting medium shall be so

646 THE SENSE OF SIGHT.

controlled as to enable objects to be seen at various
distances.

With the help of the diagram below (fig. 184), repre-
senting a vertical section of the eye from before back-
wards, the mode in which, by means of the refracting
media of the eye, an image of an object of sight is thrown
on the retina, may be rendered intelligible. The rays of
the cones of light emitted by the points A 8, and every other
point of an object placed before the eye, are first refracted,
that is, are bent towards the axis of the cone, by the
cornea ¢ c, and the aqueous humour contained between it
and the lens. The rays of each cone are again refracted

Fig. 184.

and bent still more towards its central ray or axis by the
anterior surface of the lens EE; and again as they pass
out through its posterior surface into the less dense
medium of the vitreous humour. For a lens has the power
of refracting and causing the convergence of the rays of
a cone of light, not only on their entrance from a rarer
medium into its anterior convex surface, but also at their
exit from its posterior convex surface into the rarer
medium. ,

In this manner the rays of the cones of light issuing
from the points a and B are again collected to points at a

-

REFRACTION OF RAYS OF LIGHT. 647

and }; and, if the retina Fr be situated at a and b, perfect,
though reversed, images of the points A and 8 will be
perceived: but if the retina be not at a and }, but either
before or behind that situation,—for instance, at H or ¢,—
circular luminous spots ¢ and jf, or e and o, instead of
points, will be seen; for at u the rays have not yet met,
and at c they have already intersected each other, and are
again diverging. The retina must therefore be situated
at the proper focal distance from the lens, otherwise a de-
fined image will not be formed; or, in other words, the
rays emitted by a given point of the object will not be
collected into a corresponding point of focus upon the
retina.

The means by which distinct and correct images of objects
are formed in the retina, in the various conditions in which
the eye is placed in relation to external objects, may be
separately considered under the following heads: 1, the
means for preventing indistinctness from aberration; 2,
the means for preventing it when objects are viewed at
different distances; 3, the means by which the reversed
image of an object on the retina is perceived as in its right
position by the mind.

1. Since the retina is concave, and from its centre
towards its margins gradually approaches the lens, it
follows that the images of objects situated at the sides
cannot be so distinct as those of objects nearer to the
middle of the field of vision, and of which the images are
formed at a distance beyond the lens exactly corresponding
to the situation of the retina. Moreover, the rays of a
cone of light from an object situated at the side of the
field of vision do not meet all in the same point, owing to
their unequal refraction; for the refraction of the rays
which pass through the circumference of a lens is greater
than that of those traversing its central portion. The con-
currence of these two circumstances would cause indistinct-
ness of vision, unless corrected by some contrivance. Such.

648 THE SENSE OF SIGHT.

correction is effected, in both cases, by the iris, which
forms a kind of annular diaphragm to cover the circum-
ference of the lens, and to prevent the rays from passing
through any part of the lens but its centre, which corre-
sponds to the pupil.

The image of an object will be most defined and distinct
when the pupil is narrow, the object at the proper distance
for vision, and the light abundant; so that, while a suffi-
cient number of rays are admitted, the narrowness of the
pupil may prevent the production of indistinctness of the
image by this spherical aberration or unequal refraction just
mentioned. But even the image formed by the rays pass-
ing through the circumference of the lens, when the pupil
is much dilated, as in the dark, or in a feeble light, may,
under certain circumstances, be well defined; the image
formed by the central rays being then indistinct or invisible,
in consequence of the retina not receiving these rays where
they are concentrated to a focus.

Distinctness of vision is further secured by the inner
surface of the choroid, immediately external to the retina
itself, as well as the posterior surface of the iris and the
ciliary processes, being coated with black pigment, which
absorbs any rays of light that may be reflected within the
eye, and prevents their being thrown again upon the retina
so as to interfere with the images there formed. The
pigment of the choroid is especially important in this
respect ; for the retina is very transparent, and if the sur-
face behind it were not of a dark colour, but capable of
reflecting the light, the luminous rays which had already
acted on the retina would be reflected again through it,
and would fall upon other parts of the same membrane,

producing both dazzling from excessive light, and indis- ~

tinctness of the images.

In the passage of light through an ordinary convex lens,
decomposition of each ray into its elementary coloured
parts commonly ensues, and a coloured margin appears

se

SPHERICAL ABERRATION. 649

around the image, owing to the unequal refraction which
the elementary colours undergo. In the optical instru-
ments this, which is termed chromatic aberration, is corrected
by the use of two or more lenses, differing in shape and
density, the second of which continues or increases the
refraction of the rays produced by the first, but by recom-
bining the individual parts of each ray into its original
white light, corrects any chromatic aberration which may
have resulted from the first. It is probable that the un-
equal refractive power of the transparent media in front
of the retina may be the means by which the eye is enabled
to guard against the effect of chromatic aberration. The
human eye is achromatic, however, only so long as the
image is received at its focal distance upon the retina, or
so long as the eye adapts itself to the different distances
of sight. If either of these conditions be interfered with, a
more or less distinct appearance of colours is produced.

_2. The distinctness of the image formed upon the retina
is mainly dependent on the rays emitted by each luminous
point of the object being brought to a perfect focus upon
the retina. If this focus occur at a point either in front
of, or behind the retina, indistictness of vision ensues,
with the production of a halo. The focal distance, i.e., the
distance of the point at which the luminous rays from a
lens are collected, besides being regulated by the degree of
convexity and density of the lens, varies with the distance
of the object from the lens, being greater as this is shorter,
and vice versé. Hence, since objects placed at various dis-
tances from the eye can, within a certain range, different
in different persons, be seen with almost equal distinctness,
there must be some provision by which the eye is enabled
to adapt itself, so that whatever length the focal distance
may be, the focal point may always fall exactly upon the
retina,

This power of adaptation of the eye to vision at different
distances has received the most varied explanations. It is

2

3
a
j

SIA

‘ —
ee | af

650 THE SENSE OF SIGHT.

obvious that the effect might be produced in either of two
ways, viz., by altering the convexity or density, and thus
the refracting power, either of the cornea or lens; or, by
changing the position either of the retina or of the lens, so
that whether the object viewed be near or distant, and the
focal distance thus increased or diminished, the focal point
to which the rays are converged by the lens may always be
at the place occupied by the retina. The amount of either
of these changes required in even the widest range of
vision, is extremely small. For, from the refractive powers
of the media of the eye, it has been calculated by Olbers,
that the difference between the focal!distances of the
images of an object at such a distance that the rays are
parallel, and of one at the distance of four inches, is only
about 0.143 of an inch. On this calculation, the, change
in the distance of the retina from the lens required for
vision at all distances, supposing the cornea and lens to
maintain the same form, would not be more than about
one line.

It is now almost universally believed that Helmholtz is

right in his statement that the immediate cause -of the

adaptation of the eye for objects at different distances is a
varying shape of the lens, its front surface becoming more
or less convex, according to the distance of the object
looked at. The nearer the object, the more convex does
the front : surface of the Jens become, and vice versd; the
back surface taking little or no share in the production of
the effect required. Of course, the lens has no inherent
power of contraction, and therefore its changes of outline
must be produced by some power from without; and there
seems no reason to doubt that this power is supplied by
the ciliary muscle. The exact manner, however, in which,
by its contraction, the ciliary muscle effects a change in
the shape of the crystalline lens is doubtful. The most
probable explanation of the phenomenon, however, is that
in adapting the eye for viewing near objects the ciliary

‘

ADAPTATION TO VARIOUS DISTANCES. 652

muscle contracts, and, by such contraction, diminishes the
force with which the elastic suspensory ligament of the
lens is tending to flatten it. On the latter supposition, the
lens may be supposed to be always in a state of tension
and partial flattening from the action of the suspensory
ligament ; while the ciliary muscle, by diminishing the
tension of this ligament, diminishes, to a proportional
degree, the flattening of which it is the cause. On dimi-
nution or cessation of the action of the ciliary muscle, the
lens returns, in a corresponding degree, to its former
shape, by virtue of the elasticity of its suspensory liga-
ment. In viewing near objects, the iris contracts, so that
its pupillary edge is moved a very little forwards, and the
pupil itself is contracted—the opposite effect taking place
on withdrawal of the attention from near objects, and fixing
it on those distant.

The range of distances through which persons can adapt
their power of vision
is not in all cases
the same. Some per- 4
sons possess scarcely
any power of adap-
tation, and of this
defect of vision there ®
are two kinds; one,
in which the person
can see objects dis-
tinctly only when brought close to the eye, having little
power to discern distant objects; another, in which distant
objects alone can be distinctly perceived, a small body
being almost invisible except when held at a considerable
distance from the eye. In the one case the person is said
to be short-sighted or myopic: in the other, long-sighted
or presbyopic. Myopia is caused by anything, such as
undue convexity of the lens, which increases the refracting
power of the eye, and so causes the image of the object

Fig. 185,

652 THE SENSE OF SIGHT.
to be formed at a point anterior to the retina: the defect
is remedied by the use of concave glasses. Presbyopia, or
long-sightedness, is the result of conditions the reverse of
the above, and is remedied by the use of convex glasses,
which diminish the focal distance of an image formed in
the eye.* |
3. The direction given to the rays by their refraction is
regulated by that of the central ray, or axis of the cone,
towards which the rays are bent. The image of any
point of an object is, therefore, as a rule (the exceptions to
which need not here be stated), always formed in a line
identical with the axis of the cone of light, as in the line
of B a, or a D, fig. 185: so that the spot where the image
of any point will be formed upon the retina may be deter-
mined by prolonging the central ray of the cone of light,
or that ray which traverses the centre of the pupil. Thus
A b is the axis or central ray of the cone of light issuing
from 4; Ba, the central ray of the cone of light issuing from

B; the image of a is formed at b, the image of B at a, in

the inverted position; therefore what in the object was
above is in the image below, and vice versé, —the right-hand
part of the object is in the image to the left, the left-
hand to the right. If an opening be made in an eye at
its superior surface, so that the retina can be seen through
the vitreous humour, this reversed image of any bright
object, such as the windows of the room, may be perceived
at the bottom of the eye. Or still better, if the eye of any
albino animal, such as a white rabbit, in which the coats,
from the absence of pigment, are transparent, is dissected
clean, and held with the cornea towards a window, a very
distinct image of the window completely inverted is seen
depicted on the posterior translucent wall of the eye.
Volkmann has also shown that a similar experiment may

* For details on this subject, consult the various treatises on the
Physiology and Defects of Vision.

INVERSION OF IMAGE ON RETINA. 653
be successfully performed in a living person possessed
of large prominent eyes, and an unusually transparent
sclerotica. :

No completely satisfactory explanation has yet been
offered to account for the mind being able to form a
correct idea of the erect position of an object of which an
inverted image is formed on the retina. Miller and
Volkmann are of opinion that the mind really perceives
an object as inverted, but needs no correction, since every-
thing is seen alike inverted, and the relative position of
the objects therefore remains unchanged: and the only
_ proof we can possibly have of the inversion is by experi-
ment and the study of the laws of optics. It is the same
thing as the daily inversion of objects consequent on the
revolution of the entire earth, which we know only by ob-
serving the position of the stars; and yet it is certain that,
‘ within twenty-four hours, that which was below in relation
to the stars, comes to be above. Hence it is, also, that no
discordance arises between the sensations of inverted vision
and those of touch, which perceives everything in its erect
position; for the images of all objects, even of our own
limbs, in the retina, are equally inverted, and therefore
maintain the same relative position. Even the image of
our hand, while used in touch, is seen inverted. The
position in which we see objects, we call therefore the
erect position. A mere lateral inversion of our body in a
mirror, where the right hand occupies the left of the
image, is indeed scarcely remarked: and there is but little
discordance between the sensations acquired by touch in
regulating our*movements by the image in the mirror, and
those of sight, as, for example, in tying a knot in the
erayat. There is some want of harmony here, on account
of the inversion being only lateral, and not complete in all
directions.

The perception of the erect position of objects appears,
therefore, to be the result of an act of the mind. And this

654 THE SENSE OF SIGHT.

leads us to a consideration of the several other properties
of the retina, and of the co-operation of the mind in the
several other parts of the act of vision. To these belong
not merely the act of sensation itself, and the perception
of the changes produced in the retina, as light and colours,
but also the conversion of the mere images depicted in the
retina into ideas of an extended field of vision, of proxi-
mity and distance, of the form and size of objects, of the
reciprocal influence of different parts of the retina upon
each other, the simultaneous action of the two eyes, and —
some other phenomena. :

To speak first of the ideal size of the field of vision :—The
actual size of the field of vision depends on the extent of
the retina, for only so many images can be seen at any one
time as can occupy the retina, at the same time; and thus |
considered, the retina, of which the affections are perceived
by the mind, is itself the field of vision. But to the mind
of the individual the size of the field of vision has no
determinate limits; sometimes it appears very small, at »
another time very large; for the mind has the power of
projecting the images on the retina towards the exterior.
Hence the mental field of vision is very small when the
sphere of the action of the mind is limited to impediments
near the eye: on the contrary, it is very extensive when
the projection of the images on the retina towards the
exterior, by the influence of the mind, is not impeded. It
is very small when we look into a hollow body of small
capacity held before the eyes; large when we look out
upon the landscape through a small opening; more exten-
sive when we look at the landscape through a window;
and most so when our view is not confined by any near
object. In all these cases the idea which we receive of
the size of the field of vision is very different, although its
absolute size is in all the same, being dependent on the
extent of the retina. Hence it follows, that the mind is

, constantly co-operating in the acts of vision, so that at last

——— ee

THE FIELD OF VISION. 655

it becomes difficult to say what belongs to mere sensation,
and what to the influence of the mind.

By a mental operation of this kind, we obtain a correct
idea of the size of individual objects, as well as of the
extent of the field of vision. To understand this, it will be
necessary to refer again to fig. 185, p. 651.

The angle w, included between the decussating central
rays of two cones of light issuing from different points of
an object, is called the optical angle—angulus opticus seu
visorius. This angle becomes larger, the greater the dis-
tance between the points a and B; and since the angles x
and y are equal, the distance between the points a and b
in the image on the retina increases as the angle « becomes
larger. Objects at different distances from the eye, but
having the same optical angle, e—for example, the objects
¢, d, and e,—must also throw images of equal size upon
the retina; and, if they occupy the same angle of the field
of vision, their image must occupy the same spot in the
retina.

Nevertheless, these images appear to the mind to be of
very unequal size when the ideas of distance and proximity
come into play; for, from the image a b, the mind forms
the conception of a visual space extending to e, d, or ¢, and
of an object of the size which that represented by the
image on the retina appears to have when viewed close to
the eye, or under the most usual circumstances. A land-
scape depicted on the retina, as a b, and viewed under the
angle w, is therefore conceived by the mind to have an
extent of two miles perhaps, if we know that its extent is
such, or if we infer it to be so from the number of known
objects seen at the same time. And in the same way that
the images of several different objects, viewed under the
same angle, thus appear to the mind to have a different
size in the field of vision, so the whole field of vision, which
has always the same absolute size, is interpreted by the
mind as of extremely various extent: and, for this reason

656 THE SENSE OF SIGHT.

also, the image viewed in the camera obscura is regarded
as a real landscape—as the true field of vision—although
only a small image depicted upon paper. The same mental
process gives rise to the idea of depth in the field of vision ;
this idea being fixed in our mind principally by the cir-
cumstance that, as we ourselves move forwards, different
images in succession become depicted on our retina, so that
we seem to pass between these images, which to the mind
is the same thing as passing between the objects them-
selves.

The action of the sense of vision in relation to external
objects is, therefore, quite different from that of the sense
of touch. The objects of the latter sense are immediately
present to it; and our own body, with which they come
into contact, is the measure of their size. The part of a
table touched by the hand appears as large as the part of
the hand receiving an impression from it, for a part of our
body in which a sensation is excited is here the measure
by which we judge of the magnitude.of the object. In the
sense of vision, on the contrary, the images. of objects are
mere fractions of the objects themselves realized upon the
retina, the extent of which remains constantly the same.
But the imagination, which analyzes the sensations of
vision, invests the images of objects, together with the
whole field of vision in the retina, with very varying
dimensions; the relative size of the images in pro-
portion to the whole field of vision, or of the affected
parts of the retina to the whole retina, alone remaining

unaltered.
~The direction in which an object is seen, the direction of
vision, or visual direction, depends on the part of the retina
which receives the image, and on the distance of this part
from, and its relation to, the central point of the retina.
Thus, objects of which the images fall upon the same parts
of the retina lie in the same visual direction ; and when,
by the action of the mind, the images or affections of the

‘
a Ves > et
> —_

2 a ———* |

—— ~_s - S

THE VISUAL DIRECTION. 657

retina are projected into the exterior world, the relation of
_ the images to each other remains the same.

The estimation of the form of bodies by sight is the result
partly of the mere sensation, and partly of the association
of ideas. Since the form of the images perceived by the
retina depends wholly on the outline of the part of the
retina affected, the sensation alone is adequate to the
distinction of only superficial forms of each other, as of
a square from a circle. But the idea of a solid body, as a
sphere, or a body of three or more dimensions, ¢.g., a cube,
ean only be attained by the action of the mind constructing
it from the different superficial images seen in different
positions of the eye with regard to the object; and, as
shown by Mr: Wheatstone and illustrated in the stereo-
scope, from two different perspective projections of the
body being presented simultaneously to the mind by
the two eyes. Hence, when, in adult age, sight is sud-
denly restored to persons blind from infancy, all objects in
the field of vision appear at first as if painted flat on one
surface; and no idea of solidity is formed until after
long exercise of the sense of vision combined with that of
touch.

We judge of the motion of an object, partly from the
motion of its image over the surface of the retina, and
partly from the motion of our eyes following it. If the
image upon the retina moves while our eyes and our body
are at rest, we conclude that the object is changing its
relative position with regard to ourselves. In such a case
the movement of the object may be apparent only, as when
we are standing upon a body which is in motion, such as
aship. If, on the other hand, the image does not move
with regard to the retina, but remains fixed upon the same
spot of that membrane, while our eyes follow the moving
body, we judge of the motion of the object by the sensa-
tion of the muscles in action to move the eye. If the

image moves over the surface of the retina while the mus-
a UU

658 THE SENSE OF SIGHT.

cles of the eye are acting at the same time in a manner
corresponding to this motion, as in reading, we infer that
the object is stationary, and we know that we are merely
altering the relations of our eyes to the object. Sometimes
the object appears to move when both object and eye are
fixed, as in vertigo.

The mind can, by the faculty of attention, concentrate its
activity more or less exclusively upon the senses of sight,
hearing, and touch alternately. When exclusively occupied
with the action of one sense, it is scarcely conscious of the
sensations of the others. The mind, when deeply immersed
in contemplations of another nature, is indifferent to the
actions of the sense of sight, as of every other sense. We
often, when deep in thought, have our eyes open and fixed,
but see nothing, because of the stimulus of ordinary
light being unable to excite the mind to perception
when otherwise engaged. The attention which is thus
necessary for vision, is necessary also to analyse what the
field of vision presents. The mind does not perceive all
the objects presented by the field of vision at the same
time with equal acuteness, but directs itself first to one
and then to another. The sensation becomes more intense
according as the particular object is at the time the
principal. object of mental contemplation. Any compound

Fig. 186. mathematical figure produces a different
impression according as the attention is
A directed exclusively to one or the other part
of it. Thus, in fig. 186, we may in succes-
sion have a vivid perception of the whole,
or of distinct parts only ; of the six triangles
near the outer circle, of the hexagon in the middle, or of
the three large triangles. The more numerous and varied
the parts of which a figure is composed, the more scope
does it afford for the play of the attention. Hence it is
that architectural ornaments have an enlivening effect on

——

-

ANALYSIS OF FIELD OF VISION. 659

the sense of vision, since they afford constantly fresh
subject for the action of the mind.

The duration of the sensation produced by a luminous
“impression on the retina is always greater than that of the
impression which produces it. However brief the luminous
impression, the effect on the retina always lasts for about
one-eighth of a second. ‘Thus, supposing an object in
motion, say a horse, to be revealed on a dark night by a
flash of lightning. The object would be seen apparently
for an eighth of a second, but it would not appear in
motion; because although the image remained on the
retina for this time, it was really revealed for. such an
extemely short period (the duration of a flash of lightning
being almost instantaneous) that no appreciable movement
on the part of the object could have taken place in the
period during which it was revealed to the retina of the
observer. And the same fact is proved in a reverse way.
The spokes of a rapidly revolving wheel are not seen as
distinct objects, because at every point of the field of vision
over which the revolving spokes pass, a given impression
has not faded b<fore another comes to replace it. Thus every
part of the interior of the wheel appears occupied.

The duration of the after-sensation or spectrum, produced
by an object, is greater in a direct ratio with the dura-
tion of the impression which caused it. Hence the image
of a bright object, as of the panes of a window through
which the light is shining, may be perceived in the retina
for a considerable period, if we have previously kept our
eye fixed for some time on it.

The colour of the spectrum varies with that of the object
which produced it. The spectra left by the images of
white or luminous objects, are ordinarily white or lumi-
nous; those left by dark objects are dark. Sometimes,
however, the relation of the light and dark parts in the
image may, under certain circumstances, be reversed in
the spectrum; what was bright may be dark, and what

; uv 2

660 THE SENSE OF SIGHT.

was dark may appear light. This occurs whenever the

eye, which is the seat of the spectrum of a luminous object,

Fig, 187. is not closed, but fixed

upon another bright or —

red white surface, as a white

wall, or a sheet of white

ey violet ‘paper. Hence the spectrum

Sel of the sun, which, while

ie light is excluded from the

yellow Alus eye is luminous, appears

black or grey when the

aioe eye is directed upon a

white surface. The explanation of this is, that the part

of the retina which has received the luminous image

remains for a certain period afterwards in an exhausted or

less sensitive state, while that which has received a dark

image is in an unexhausted, and therefore much more
excitable condition.

The ocular spectra which remain after the impression of

coloured objects upon the retina are always coloured; and

* Fig. 187. A circle showing the various simple and compound
colours of light, and those which are complemental of each other, ¢.¢.,
which, when mixed, produce a neutral grey tint. The three simple
colours, red, yellow, and blue, are placed at the angles of an equilateral
triangle ; which are connected together by means of acircle; the mixed
colours, green, orange, and violet, are placed intermediate between the
corresponding simple or homogeneous colours ; and the complemental
colours, of which the pigments, when mixed, would constitute a grey,
and of which the prismatic spectra would together produce a white light,
will be found to be placed in each case opposite to each other, but con-
nected by a line passing through the centre of the circle. The figure
is also useful in showing the further shades of colour which are com-
plementary of each other. Ifthe circle be supposed to contain every
transition of colour between the six marked down, those which, when
united, yield a white or grey colour, will always be found directly
opposite to each other ; thus, for example, the intermediate tint between
orange and red is complemental of the middle tint between green and
blue,

ee

COMPLEMENTARY COLOURS. 661

their colour is not that of the object, or of the image pro-
duced directly by the object, but the opposite, or comple-
mental colour. The spectrum of a red object is, therefore,
green; that of a green object, red; that of violet, yellow;
that of yellow, violet, and so on. The reason of this is
obvious. The part of the retina which receives, say, a red
image, is wearied by that particular colour, but remains
sensitive to the other rays which with red make up white
light; and, therefore, these by themselves reflected from a
white object produce a green hue. If, on the other hand,
the first object looked at be green, the retina being tired
of green rays, receives a red image when the eye is turned
to a white object. And so with the other colours; the
retina while fatigued by yellow rays will suppose an object
to be violet, and vice versé; the size and shape of the
spectrum corresponding with the size and shape of the
original object looked at. The colours which thus recipro-
cally excite each other in the retina are those placed at
opposite points of the circle in fig. 187.

Of the Reciprocal Action of different Parts of the Retina on
each other.

Although each elementary part of the retina represents
a distinct portion of the field of vision, yet the different
elementary parts, or sensitive points, of that membrane,
have a certain influence on each other ; the particular con-
dition of one influencing that of another, so that the image
perceived by one part is modified by the image depicted in
the other. The phenomena, which result from this relation
between the different parts of the retina, may be arranged
in two classes; the one including those where the condition
existing in the greater extent of the retina is imparted
to the remainder of that membrane; the other, consisting
of those in which the condition of the larger portion of the
retina excites, in the less extensive portion, the opposite
condition.

662 THE SENSE OF SIGHT.

1. When two opposite impressions occur in contiguous
parts of an image on the retina, the one impression is,
under certain circumstances, modified by the other. If
the impressions occupy each one-half of the image, this
does not take place; for in that case, their actions are
equally balanced. But if one of the impressions occupies
only a small part of the retina, and the other the greater
part of its surface, the latter may, if long continued, ex-
tend its influence over the whole retina, so that the
opposite less extensive impression is no longer perceived,
and its place becomes occupied by the same sensation as
the rest of the field of vision: Thus, if we fix the eye
for some time upon a strip of coloured paper lying upon
a white surface, the image of the coloured object,
especially when it falls on the lateral parts of the retina,
will gradually disappear, and the white surface be seen in
its place.

2. In the second class of phenomena, the affection of
one part of the retina influences that of another part, not
in such a manner as to obliterate it, but so as to cause it
to become the contrast or opposite of itself. Thus a grey
spot upon a white ground appears darker than the same
tint of grey would do if it alone occupied the whole field
of vision, and a shadow is always rendered deeper when
the light which gives rise to it becomes more intense,
owing to the greater contrast. The former phenomena
ensue gradually, and only after the images have been
long fixed on the retina; the latter are instantaneous in
their production, and are permanent.

In the same way, also, colours may be produced by con-
trast. Thus, a very small dull-grey strip of paper, lying
upon an extensive surface of any bright colour, does not
appear grey, but has a faint tint of the colour which is the
complement of that of the surrounding surface (see page
661). A strip of grey paper upon a green field, for
example, often appears to have a tint of red, and when

MODIFICATION OF VISUAL IMPRESSIONS. 663

lying upon a red surface, a greenish tint; it has an orange-
coloured tint upon a bright blue surface, and a blueish
tint upon an orange-coloured surface ; a yellowish colour
upon a bright violet, and a violet tint upon a bright
yellow surface. The colour excited thus, as a contrast to
the exciting colour, being wholly independent of any rays
of the corresponding colour acting from without upon the
retina, must arise as an opposite or antagonistic condition
of that membrane; and the opposite conditions of which
_ the retina thus becomes the subject would seem to balance
each other by their reciprocal reaction. A necessary con-
dition for the production of the contrasted colours is, that
the part of the retina in which the new colour is to be
excited, shall be in a state of comparative repose ; hence
the small object itself must be grey. A second condition
is, that the colour of the surrounding surface shall be very
bright, that is, it shall contain much white light.

The retina corresponding to the point of entrance of the
optic nerve is completely insensible to the impressions of
light. The phenomenon itself is very readily shown. If
we direct one eye, the other being closed, upon a point at
such a distance to the side of any object, that the image
of the latter must fall upon the retina at the point of
entrance of the optic nerve, this image is lost either

8 +
instantaneously, or very soon. If, for example, we close
the left eye, and direct the axis of the right eye steadily
towards the circular spot here represented, while the page
is held at a distance of about six inches from the eye,
both dot and cross are visible. On gradually increasing the
distance between the eye and the object, by removing
the book farther and farther from the face, and still
keeping the right eye steadily on the dot, it will be found
that suddenly the cross disappears from view, while on
removing the book still farther, it suddenly comes in sight

664 THE SENSE OF SIGHT.

again. The cause of this phenomenon is simply that the-
portion of retina which is occupied by the entrance of the-
optic nerve, is quite blind; and therefore that when it
alone occupies the field of vision, objects cease to be
visible.

Of the Simultaneous Action of the two Eyes.

Although the sense of sight is exercised by two organs,
yet the impression of an object conveyed to the mind is.
single. Various theories have been advanced to account
for this phenomenon. By Gall, it was supposed that we
do not really employ both eyes simultaneously in vision,
but always see with only one at atime. This especial
employment of one eye in vision certainly occurs in
persons whose eyes are of very unequal focal distance, but
in the majority of individuals both eyes are simultaneously
in action in the perception of the same object; this is.
shown by the double images seen under certain conditions.
If two fingers be held up before the eyes, one in front of
the other, and vision be directed to the more distant, so.
that it is seen singly, the nearer will appear double ; while,
if the nearer one be regarded, the most distant will be
seen double; and one of the double images in each case
will be found to belong to one eye, the other to the other
eye. |
Single vision results only when certain parts of the two.
retinze are affected simultaneously ; if different parts of
the retinze receive the image of the object, it is seen
double. The parts of the retin in the two eyes which
thus correspond to each other in the property of referring
the images which affect them simultaneously to the same
spot in the field of vision are, in man, just those parts
which would correspond to each other, if one retina were
placed exactly in front of, and over the other (as in
fig. 188; c). Thus, the outer lateral portion of one eye
corresponds to, or, to use a better term, is identical with,

SS he eee st ri

“e.

SINGLE VISION. - 663

the inner portion of the other eye; or a of the eye A (fig. .
188) with a’ of the eye s. The upper part of one retina is

l : . ° h
also identical with the Fig. 188.

upper part of the other ; a 53 = 7
and the lower parts of cde
the two eyes are iden- e ¢
tical with each other. ae: ) 3

This is proved by — Way
a single experiment.

Pressure upon any part

of the ball of the eye, so as to affect the retina, produces
a luminous circle, seen at the opposite side of the field,
of vision to that on which the pressure is made. If, now,
in a dark room, we press with the finger at the upper part
of one eye, and at the lower part of the other, two lumi-
nous circles are seen, one above the other; so, also, two
figures are seen when pressure is made simultaneously on
the two outer or the two inner sides of both eyes. It is
certain, therefore, that neither the upper part of one
retina and the lower part of the other are identical, nor
the outer lateral parts of the two retine, nor their inner
lateral portions. But if pressure be made with the fingers
upon both eyes simultaneously at their lower part, one
luminous ring is seen at the middle of the ‘upper part of
the field of vision; if the pressure be applied to the upper
part of both eyes, a single luminous circle is seen in the
middle of the field of vision below. So, also, if we press
upon the outer side a of the eye a, and upon the inner side
a’ of the eye 8, asingle spectrum is produced, and is ap-
parent at the extreme right of the field of vision; if upon
the point b of one eye, and the point b’ of the other, a
single spectrum is seen to the extreme left.

The spheres of the two retine may, therefore, be re-
garded as lying one over the other, as in o, fig. 188; so
that the left portion of one eye lies over the identical left
portion of the other eye, the right portion of one eye over

666 THE SENSE OF SIGHT.

the identical right portion of the other eye; and with the
upper and lower portions of the two eyes, a lies over a’, b
over b’, and overc’. The points of the one retina inter-
mediate between a and c, are again identical with the
corresponding points of the other retina between a’ and ¢’ ;
those between 6 and c of the one retina, with those
between b’ and c’ of the other. In short, all other parts
are non-identical: and, when they are excited to action,
the effect is the same as if the impressions were made on
different parts of the same retina: and the double images
belonging to the eyes a and B, are seen at exactly the same
distance from each other as exists between the image of
the eye a and the part of the retina of the eye a which
corresponds to, or is identical with, the seat of the second
image in the eye B; or, to return to the figure already
used in illustration (fig. 188), if a of one eye be affected,
and b’ of the other, the distances of the two images a and b’
will, inasmuch as a is identical with a’, and b’ with }, lie at
exactly the same distance from each other as images pro-
duced by impressions on the points a b of the one eye, or a’
b’ of the other.

In application of these results to the phenomena of
vision, if the position of the eyes with regard to a lumi-
nous object ‘be such that similar images of the same
object fall on identical parts of the two retins, as occurs
when the axes meet in some one point, the object is seen
single; if otherwise, as in the various forms of squinting,
two images are formed, and double vision results. Ifthe axes
of the eyes, a and B (fig. 189), he so directed that they meet
at a, an object at a will be seen singly, for the point a of the
one retina, and a’ of the other, are identical. So, also, if
the object B be so situated that its image falls in both eyes
at the same distance from the central point of the retina,
—namely, at b in the one eye, and at b’ in the other,—f
will be seen single, for it affects identical parts of the two
retin. The same will apply to the object 7’.

SINGLE VISION. 667

In quadrupeds, the relation between the identical and
non-identical parts of the retinze cannot be the same as in
man; for the axes
of their eyes gene-
rally diverge, and
can never be made
to meet in one point
of an object. When
an animal regards
an object situated
directly in front of
it, the image of the
object must fall, in
both eyes, on the
outer portion of the
retine. Thus the
image of the object
a (fig. 191) will fall at a’ in one, and at a” in the other : and
these points a’ and a’’ must be identical. So, also, for dis-
tinct and single vision of objects, b orc, the points b’ and b”,
or c’ ¢’’, in the two retine, on which the images of these
objects fall, must be identical. All points of the retina in
each eye which receive rays of light from lateral objects
only, can have no corresponding identical points in the
retina of the other eye; for otherwise two objects, one
situated to the right and the other to the left, would appear
to lie in the same spot of the field of vision. It is probable,
therefore, that there are, in the eyes of animals, parts of
the retinze which are identical, and parts which are not
identical, i.c., parts in one which have no corresponding
parts in the other eye. And the relation of the two retin
to each other in the field of vision may be represented as
in fig. 190. *

The cause of the impressions on the identical points of
the two retine giving rise to but one sensation, and the
perception of a single image, must either lie in the struc-

Fig. 189.

668 — THE SENSE OF SIGHT.

tural organization of the deeper or cerebral portion of the
visual apparatus, or be the result of a mental operation ;
for in no other case is it the property of the corresponding
nerves of the two sides of the body to refer their sensa-
tions as one to one spot.

Fig. 190.

Cts om
x
P—.

Sy a” ry /
eee ineo™ ae,
Bs of

Many attempts have been made to explain this remark-

able relation between the eyes, by referring it to anatomi-
cal relation between the optic nerves. The circumstance
of the inner portion of the fibres of the two optic nerves
decussating at the commissure, and passing to the eye of
the opposite side, while the outer portion of the fibres con-
tinue their course to the eye of the same side, so that the
left side of both retinze is formed from one root of the
nerves, and the right side of both retine: from the other
root, naturally lead to an attempt to explain the pheno-
menon by this distribution of the fibres of the nerves.
And this explanation is favoured by cases in which the
entire of one side of the retina, as far as the central point
in both eyes, sometimes becomes insensible. But Miller
shows the inadequateness of this theory to explain the

4 7
ee

ae

eS ae ai

SINGLE VISION. 669

phenomenon, unless it be supposed that each fibre in each
cerebral .portion of the optic nerve divides in the optic
commissure into two branches for the identical points of
the two retinee, as is shown in fig. 192. But there is no
foundation for such supposition. —

By another theory it is assumed that each optic nerve
contains exactly the same number of fibres as the other,
and that the corresponding fibres of the two nerves are
united in the sensorium (as in fig. 193). But in this

Fig. 192. Fig. 193. Fig. 194.

theory no accourt is taken of the partial decussation of the
fibres of the nerves in the optic commissure.
According to a third theory, the fibres a and a’, fig. 194,

coming from identical points of the two retine:, are in the

optic commissure brought into one optic nerve, and in the
brain either are united by a loop, or spring from the same
point. ‘The same disposition prevails in the case of the
identical fibres 6 and b’. According to this theory, the

left half of each retina would be represented in the left

hemisphere of the brain, and the right half of each retina
in the right hemisphere.

Another explanation is founded on the fact, that at the
anterior part of the commissure of the optic nerve, certain
fibres pass across from the distal portion of one nerve to
the corresponding portion of the other nerves, as if they
were commissural fibres forming a connection between tlie

670 THE SENSE OF SIGHT.

retinee of the two eyes. It is supposed, indeed, that these
fibres may connect the corresponding parts of the two
retinee, and may thus explain their unity of action; in the
same way that corresponding parts of the cerebral hemi-
spheres are believed to be connected together by the com-
missural fibres of the corpus callosum, and so enabled to
exercise unity of function.

But, on the whole, it is more probable, that the power
of forming a single idea of an object from a double im-
pression conveyed by it to the eyes is the result of a mental
act. This view is supported by the same facts as those
employed by Professor Wheatstone to show that this power
is subservient to the purpose of obtaining a right percep-
tion of bodies raised in relief. When an object is placed

Fig. 195.

Be

so near the eyes that to view it the optic axes must con-
verge, a different perspective projection of it is seen by
each eye, these perspectives being more dissimilar as the
convergence of the optic axes becomes greater. Thus, if
any figure of three dimensions, an outline cube, for ex-
ample, be held at a moderate distance before the eyes,
and viewed with each eye successively, while the head is
kept perfectly steady, a (fig. 195) will be the picture pre-
sented to the right eye, and 3 that seen by the left eye.
Mr. Wheatstone has shown that on this circumstance
depends in a great measure our conviction of the solidity
of an object, or of its projection in relief. If different
perspective drawings of a solid body, one representing the

THE STEREOSCOPE. — 671

image seen by the right eye, the other that seen by the
left (for example, the drawing of a cube a, B, fig. 195), be
presented to corresponding parts of the two retins, as
may be readily done by means of the stereoscope, an instru-
ment invented by Professor Wheatstone for the purpose,
the mind will perceive not merely a single representation
of the object, but a body projecting in relief, the exact
counterpart of that from which the drawings were made.

SENSE OF HEARING.

Anatomy of the Organ of Hearing.

For descriptive-purposes, the ear, or organ of hearing,
is divided into three parts, the external, the middle, and
the internal ear. The two first are only accessory to the third
or internal ear, which contains the essential parts of an
organ of hearing. The accompany-
ing figure shows very well the
relation of these divisions,—one to
the other (fig. 196).

The external ear consists of the
pinna or auricle, and the external
auditory canal or meatus. The prin-
cipal parts of the pinna are two
prominent rims enclosed one within
the other (helix and antiheliz), and
enclosing a central hollow named
the concha ; in front of the concha,
a prominence directed backwards,
the tragus, and opposite to this, one |
directed forwards, the antitrayus. From the concha, the

Fig. 196.*

4) i:
yy i” yyy

2

* Fig. 196. Outer surface of the pinna of the right auricle. 2.—1,
helix ; 2, fossa of the helix; 3, antihelix ; 4, fossa of the antihelix ;
5, antitragus ; 6, tragus; 7, concha; 8, lobule.

672 THE SENSE OF HEARING.

auditory canal, with a slight arch directed upwards, pdassés
inwards and a little forwards to the membrana tympani,

Fig. 197.*

to which it thus serves to convey the vibrating air. Its

* Fig. 197. Diagrammatic view from before of the parts composing
the organ of hearing of the left side (after Arnold). . The temporal bone
of the left side, with the accompanying soft. parts, has been detached
from the head, and a section has been carried through it transversely, so
as to remove the front of the meatus externus, half the tympanic mem-
brane, the upper and anterior wall of the tympanum and Eustachian
tube. The meatus internus has also been opened, and the bony labyrinth
exposed by the removal of the surrounding parts of the petrous bone.
1. the pinnaand lobe ; 2, 2’, meatus externus; 2’, membrana tympani ;
3, cavity of the tympanum ; 3’, its opening backwards into the mastoid
cells ; between 3 and 3’, the chain ofsmall bones ; 4, Eustachian tube ;
5, meatus internus containing the facial (uppermost) and the auditory
nerves ; 6, placed on the vestibule of the labyrinth above the fenestra
ovalis: a, apex of the petrous bone ; 0, internal carotid artery ; ¢, styloid
process; d, facial nerve issuing from the stylo-mastoid foramen ; e,

mastoid process ; f, squamous part of the bone covered by integument,

ete.

THE MIDDLE EAR. 673

outer part consists of fibro-cartilage continued from the
concha; its inner part of bone. Both are lined by skin
continuous with that of the pinna, and extending over the
outer part of the membrana tympani. Towards the outer
part of the canal are fine hairs and sebaceous glands,
while deeper in the canal are small glands, resembling
the sweat-glands in structure, which secrete a peculiar
yellow substance called cerwmen, or ear-wax.

The middle ear, or tynpanum (3, fig. 197) is separated by
the membrana tympani from the external auditory canal.
It is a cavity in the temporal bone, opening through its
anterior and inner wall into the Eustachian tube, a
cylindriform flattened canal, dilated at both ends, com- |
posed partly of bone and partly of cartilage, lined with
mucous membrane, and forming a communication between
the tympanum and the pharynx. It opens into the cavity
of the pharynx just behind the posterior aperture of the
nostrils. The cavity of the tympanum communicates
posteriorly with air-cavities, the mastoid cells in the mas-
toid process of the temporal bone; but its only opening
to the external air is through the Eustachian tube (4, fig.
197). The walls of the tympanum are osseous, except
where apertures in them are closed with membrane, as at
the fenestra, rotunda, and fenestra ovalis, and at the outer
part where the bone is replaced by the membrana tympani.
The cavity of the tympanum is lined with mucous mem-
brane, the epithelium of which is ciliated and continuous
with that of the pharynx. It contains a chain of small
bones (ossicula auditus), which extends from the membrana
‘tympani to the fenestra ovalis.

The membrana tympani is placed in a slanting direction
at the bottom of the external auditory canal, its plane
being at an angle of about 45° with the lower wall of the
canal. Itis formed chiefly of a tough and tense fibrous
membrane, the edges of which are set in a bony groove;
its outer surface is covered with a continuation of the

x xX

674 THE SENSE OF HEARING.

cutaneous lining of the auditory canal, its inner surface
with part of the ciliated mucous membrane of the tym-
panum.

The small bones or ossicles of the ear are three, named
malleus, incus, and stapes. The malleus, or hammer-bone, is
attached by a long slightly-curved process, called its
handle, to the membrana tympani; the line of attach-
ment being vertical, including the whole length of the
handle, and extending from the upper border to the centre
of the membrane. The head of the malleus is irregularly
rounded; its neck, or the line of boundary between it and
the handle, supports two processes; a short conical one,
which receives the insertion of the tensor tympani, and a
slender one, processus gracilis, which extends forwards, and
to which the laxator tympani muscle is attached. The ineus,
or anvil-bone, shaped like a bicuspid molar tooth, is
articulated by its broader part, corresponding with the
surface of the crown of a tooth, to the malleus. Of its.
two fang-like processes, one, directed backwards, has a
free end, the other, curved downwards and more pointed,
articulates by means of a roundish tubercle, formerly
called os orbiculare, with the stapes, a little bone shaped
exactly like a stirrup, of which the base or bar fits into.
the fenestra ovalis. To the neck of the stapes, a short
process, corresponding with the loop of the stirrup, is
attached the stapedius muscle.

The bones of the ear are covered with mucous mem-
brane reflected over them from the wall of the tympanum ;
and are moveable both altogether and one upon the other.
The malleus moves and vibrates with every movement and
vibration of the membrana tympani, and its movements
are communicated through ‘the incus to the stapes, and
through it to the membrane closing the fenestra ovalis.
The malleus, also, is moveable in its articulation with the
incus; and the membrana tympani moving with it is
altered in its degree of tension by the laxator and tensor

~

pes THE LABYRINTH. — * Ome

tympani muscles. The stapes is moveable on the process
of the incus, when the stapedius muscle acting draws it
backwards. ,

The proper organ of hearing is formed by the distribu-
tion of the auditory nerve within the internal ear, or
labyrinth of the ear, a set of cavities within the petrous
portion of the temporal bone. The bone which forms the
walls of these cavities is denser than that around it, and

Fig. 198.* Fig. 199.+

‘* Fig. 198. Right bony labyrinth, viewed from the outer side (after
Sémmerring). %!.—The specimen here represented is prepared by sepa-
rating piecemeal the looser substance of the petrous bone from the dense
walls which immediately enclose the labyrinth. 1, the vestibule ; 2,
fenestra ovalis ; 3, superior semicircular canal ; 4, horizontal or external
canal; 5,, posterior canal ; *, ampulle of the semicircular canals; 6,
first turn of the cochlea; 7, second turn ; 8, apex; 9, fenestra rotunda.
The smaller figure in outline below shows the natural size.

{ Fig. 199. View of the interior of the left labyrinth (from Sommer-
ving). 2%4.—The bony wall of the labyrinth is removed superiorly and
externally. 1, fovea hemielliptica ; 2, fovea hemispherica ; 3, common
opening of the superior and posterior semicircular canals ; 4, opening
of the aqueduct of the vestibule; 5, the superior, 6, the posterior, and
7, the external semicircular canals ; 8, spiral tube of the cochlea (scala
tympani); 9, opening of the aqueduct of the cochlea ; 10, placed on
the lamina spiralis in the scala vestibuli.

phe. Be

676 _ THE SENSE OF HEARING.

forms the osseous labyrinth; the membrane within the
cavities forms the membranous labyrinth. 'The membranous
labyrinth contains a fluid called endolymph ; while outside
it, between it and the osseous labyrinth, is a fluid called
perilymph (see p. 678).

The osseous labyrinth consists of three principal parts,
namely, the véstibule, the cochlea, and the semicircular canals.
The vestibule is the middle cavity of the labyrinth, and the

central organ of the whole auditory apparatus. It presents, |

in its inner walls, several openings for the entrance of the
divisions of the auditory nerve; in its outer wall, the fenestra
ovalis (2, fig. 198), an opening filled by the base of the stapes,
one of the small bones of the ear; in its posterior and
superior walls, five openings by which the semicircular
canals communicate with it: in its anterior wall, an open-
ing leading into the cochlea. The hinder part of the inner
wall of the vestibule also presents an opening, the orifice
of the aqueductus vestibuli, a canal leading to the posterior
margin of the petrous bone, with uncertain contents and
unknown purpose.

The semicircular canals (figs. 198, 199) are three arched _

cylindriform bony canals, set in the substance of the petrous
bone. ‘They all open at both ends into the vestibule (two of
them first coalescing). The ends of each are dilated just
before opening into the vestibule; and one end of each being
more dilated than the other, is called an ampulla. Two of
the canals form nearly vertical arches; of these the superior
is also anterior; the posterior is inferior; the third canal
is horizontal, and lower and shorter than the others.

The cochlea (6, 7, 8 , fig. 198, and fig. 200), a small
organ, shaped like a common snail-shell, is seated in
front of the vestibule, its base resting on the bottom
of the internal meatus, where some apertures transmit to
it the cochlear filaments of the auditory nerve. In its
axis, the cochlea is traversed by a conical column, the
modiolus, around which a spiral canal winds with about two

~

THE LABYRINTH. 6 77

turns and a half from the base to the apex. At the apex
of the cochlea the canal is closed; at the base it presents
three openings, of which
one, already mentioned,
communicates with the ves-
tibule; another, called /e-
nestra rotunda, is separated
by a membrane from the
cavity of the tympanum ;
the third is the orifice of
the aqueductus cochlea, a
canal leading to the jugular fossa of the petrous bone, and
corresponding, at least in obscurity of purpose and origin,
to the aqueeductus vestibuli. The spiral canal is divided into
two passages, or scalee, by a partition of bone and membrane,
the lamina spiralis. The osseous part or zone of this lamina
is connected with the modiolus; the membranous part,
with a muscular zone, according to Todd and Bowman,
forming its outer margin, is attached to the outer wall of
the canal. Commencing at the base of the cochlea, be-
tween its vestibular and tympanic openings, they form a
partition between these apertures; the two scale are,
therefore, in correspondence with this arrangement, named
scala vestibuli and scala tympani. At the apex of the cochlea
the lamina spiralis ends in a small hamulus, the inner and
concave part of which, being detached from the summit of
she modiolus, leaves a small aperture named helicotrema, by
which the two scale, separated in all the rest of their
length, communicate. 7

Besides the scala vestibuli and scala tympani, there is a third
space between them, in the substance of the lamina spiralis,
called the scala media, or canalis membranacea, and in this are

* Fig. 200. View of the osseous cochlea divided through the middle
(from Arnold). %—1, central canal of the modiolus ; 2, lamina spiralis
ossea ; 3, scala tympani; 4, scala vestibuli; 5, porous substance of the
modiolus near one of the sections of the canalis spiralis modioli.

678 > THE SENSE OF HEARING.

some peculiar club-shaped little bodies called the rods of Corti,
set up on end, with their big extremities upwards, and leaning
against each other at the top—a section, therefore, having
the appearance of the gable-end of a house.. On their
outer part are numerous cells of various shapes. The
regularity with which the little rods of Corti are arranged,
has caused them to be compared to rows of keys in a piano.

In close relation with these rods and the cells outside
them, and probably projecting also by free ends into the
little triangular canal containing fluid which is between
the rods, are filaments of the auditory nerve.

The membranous labyrinth corresponds generally with the
form of the osseous labyrinth, so far as regards the vesti-
bule and semicircular canals, but is separated from the
walls of these parts by fluid, except where the nerves enter
into connection within it. In the cochlea, the membranous
labyrinth completes the septum between the two scale, and
encloses a separate spiral canal, the canalis membranacea.
As already mentioned, the membranous labyrinth contains
a fluid called endolymph ; and between its outer surface and
the inner surface of the walls of the vestibule and semi-
circular canals is another collection of similar fluid, called
perilymph : so that all the sonorous vibrations impressing

the auditory nerves on these parts of the internal ear are_

conducted through fluid to a membrane suspended in and
containing fluid. The fluid in the scale of the cochlea
is continuous with the perilymph in the vestibule and
semicircular canals, and there is no fluid external to its
lining membrane.

The vestibular portion of the membranous labyrinth

comprises two, probably communicating cavities, of which
the larger and upper is named the utriculus ; the lower, the
sacculus. Into the former open the orifices of the mem-
branous semicircular canals; into the latter the canalis
membranacea of the cochlea. The membranous labyrinth
of all these parts is laminated, transparent, very vascular,

THE LABYRINTH. — 679

and covered on the inner surface with nucleated cells, of
which those that line the ampulle are prolonged into stiff
hair-like processes; the same appearance, but to a much
less degree, being visible in the wtricle and saccule. | In the
cavities of the utriculus and sacculus are small masses of
calcareous particles, otoconia or: otolithes; and the same,
although in more minute quantities, are to be found in the
interior of other parts of the membranous labyrinth.

The auditory nerve, for the appropriate exposure of
whose filaments to sonorous vibrations all. the organs now
described are provided, is characterised as a nerve of
special sense by its softness (whence it derived its name
of portio mollis of the seventh pair), and by the fineness of
its component fibres. It enters the labyrinth of the ear
in two divisions; one for the vestibule and semicircular
canals, and the other for the cochlea. The branches for
the vestibule spread out and radiate on the inner surface
of the membranous labyrinth : their exact termination is
unknown. ‘Those for the semicircular canals pass into the
ampulle, and form, within each of them, a forked projec-
tion which corresponds with a septum in the interior of
_ the ampulla. The branches of the cochlea enter it through
orifices at the base of the modiolus, which they ascend, and
thence successively pass into canals in the osseous part
of the lamina spiralis. In the canals of this osseous part
or zone, the nerves are arranged in a plexus, containing
ganglion cells. Their ultimate termination is not known
with certainty ; but some of them, without doubt, end in
the organ of Corti, probably in cells.

| Physiology of Hearing.

The acoustic portion of the physiology of hearing is thus
illustrated by Miiller : chiefly in applications of the results
of his experiments on the conduction of sonorous vibra-
tions through various combinations of air, water, and solid
substances, especially membrane.

680 THE SENSE OF HEARING.

All the acoustic contrivances of the organ of hearing are
means for conducting the sound, just as the optical appa-
ratus of the eye area media for conducting the light. Since
all matter is capable of propagating sonorous vibrations,
the simplest conditions must be sufficient for mere hear-
ing; for all substances surrounding the auditory nerve
would communicate sound to it. In the eye a certain
construction was required for directing the rays or undula-
tions of light in such a manner that they should fall upon
the optic nerve with the same relative disposition as that
with which they issued from the object. In the sense of
hearing this is not requisite. Sonorous vibrations, having
the most various direction and the most unequal rate of
succession, are transmitted by all media without modifica-
tion, however manifold their decussations; and, wherever
these vibrations or undulations fall upon the organ of
hearing and the auditory nerves, they must cause the
sensation of corresponding sounds. The whole develop-
ment of the organ of hearing, therefore, can have for its
object merely the rendering more perfect the propagation of
the sonorous vibrations, and their multiplication by re-
sonance ; and, in fact, all the acoustic apparatus of the organ.
may be shown to have reference to these two principles.

Functions of the External Ear.

The external auditory passage influences the propaga-
tion of sound to the tympanum in three ways:—1I, by
causing the sonorous undulations, entering directly from
the atmosphere, to be transmitted by the air in the passage
immediately to the membrana tympani, and thus pre-
venting them from being dispersed; 2, by the walls of the
passage conducting the sonorous undulations imparted to
the external ear itself, by the shortest path to the attach-
ment of the membrana tympani, and so to this membrane ;
3, by the resonance of the column of air contained within
the passage.

FUNCTIONS OF THE EXTERNAL EAR. 681

As a conductor of undulations of air, the external
auditory passage receives the direct undulations of the
atmosphere, of which those that enter in the direction of
its axis produce the strongest impressions. The undula-
tions which enter the passage obliquely are reflected by
its parietes, and thus by reflexion reach the membrana
tympani. By reflexion, also, the external meatus receives
the undulations which impinge upon the concha of the
external ear, when their angle of reflexion is such that
they are thrown towards the tragus. Other sonorous
undulations, again, which could not enter the meatus from
the external air either directly or by reflexion, may still be
brought into it by inflexion; undulations, for instance,
whose direction is that of the long axis of the head, and
which pass over the surface of the ear, must, in accord-
ance with the laws of inflexion, be bent into the external
meatus by its margins. But the action of those undula-
tions which enter the meatus directly are most intense ; and
hence we are enabled to judge of the point whence sound
comes, by turning one ear in different directions, till it is
directed to the point whence the vibrations may pass directly
into the meatus, and produce the strongest impressions.

' The walls of the meatus are also solid conductors of
sound; for those vibrations which are communicated to
the cartilage of the external ear, and not reflected from it,
are propagated by the shortest path through the parietes of
the passage to the membrana tympani. Hence, both ears,
being close stopped, the sound of a pipe is heard more dis-
tinctly when its lower extremity, covered with a membrane,
is applied to the cartilage of the external ear itself, than
when it is placed in contact with the surface of the head.

Lastly, the external auditory passage is important, inas-
much as the air which it contains, like all insulated masses
of air, increases the intensity of sounds by resonance.
To convince ourselves of this, we need only lengthen the
passage by affixing to it another tube: every sound that is

682 THE SENSE OF HEARING.

heard, even the sound of our own voice, is then much
increased in intensity.

The action of the cartilage of the external ear upon
sonorous vibrations is partly to reflect them, and p2rtly to
condense and conduct them to the parietes of the external
passage. With respect to its reflecting action, the concha
is the most important part, since it directs the reflected
undulations towards the tragus, whence they are reflected
into the auditory passage. The other inequalities of the
external ear do not promote hearing by reflexion; and, if
the conducting power of the cartilage of the ear were left
out of consideration, they might be regarded as destined
for no particular use; but receiving the impulses of the
air, the cartilage of the external ear, while it reflects a
part of them, propagates within itself and condenses the
rest, as all other solid and elastic bodies would do. Thus,
the sonorous vibrations which it receives by an extended
surface, are conducted by it to its place of attachment.
In consequence of the connection of the parietes of the
auditory passage with the solid parts of the whole head,
some dispersion of the undulations will result; but the
points of attachment of the membrana tympani will receive
them by the shortest path, and will as certainly com-
municate them to that membrane, as the solid sides of a
drum communicate sonorous undulations to the parchment
head, or the bridge of a musical string, its vibrations to
the string.

Regarding the cartilage of the external ear, therefore,
as a conductor of sonorous vibrations, all its inequalities,
elevations, and depressions, which are useless with regard
to reflexion, become of evident importance; for those
elevations and depressions upon which the undulations
fall perpendicularly, will be affected by them in the most
intense degree ; and in consequence of the various form
and position of these inequalities, sonorous undulations,
in whatever direction they may come, must fall perpen-

FUNCTIONS OF THE MIDDLE EAR. 683

dicularly upon the tangent of some one of them. This
affords an explanation of the extraordinary form given to
this part.

Functions of the Middle Ear: the Tympanum, Ossicula, and
Fenestra.

In animals living in the atmosphere, the sonorous vibra-
_ tions are conveyed to the auditory nerve by three different
media in succession; namely, the air, the solid parts of the
body of the animal and of the auditory apparatus, and
the fluid of the labyrinth.

Sonorous vibrations are imparted too imperfectly from
air to solid bodies, for the propagation of sound to the
internal ear to be adequately effected by that means alone;
yet already an instance of its being thus propagates has
been mentioned.

In passing from air directly into water, sonorous ae
tions suffer also a considerable diminution of their strength; _
but if a tense membrane exists between the air and the
water, the sonorous vibrations are communicated from the
former to the latter medium with very great intensity.
This fact, of which Miller gives experimental proof,
furnishes at once an explanation of the use of the fenestra
rotunda, and of the membrane closing it. They are the
means of communicating, in full intensity, the vibrations
of the air in the tympanum to the fluid of the labyrinth.
This peculiar property of membranes is the result, not of
their tenuity alone, but of the elasticity and capability of
displacement of their particles; and it is not impaired
when, like the membrane of the fenestra rotunda, they are
not impregnated with moisture.

Sonorous vibrations are also communicated without any
perceptible loss of intensity from the. air to the water,
when to the membrane forming the medium of communi-
cation, there is attached a short, solid body, which occupies
the greater part of its surface, and is alone in contact

684 THE SENSE OF HEARING.,

with the water. This fact elucidates the action of the
fenestra ovalis, and of the plate of the stapes which
occupies it, and, with the preceding fact, shows that both
fenestrea—that closed by membrane only, and that with
which the moveable stapes is connected—transmit very
freely the sonorous vibrations from the air to the fluid of
the labyrinth.

A small, solid body, fixed in an opening by means of a ~
border of membrane, so as to be moveable, communicates
sonorous vibrations from air on the one side, to water, or
the fluid of the labyrinth, on the other side, much better
than solid media not so constructed. But the propagation
of sound to the fluid is rendered much more perfect if the
solid conductor thus occupying the opening, or fenestra
ovalis, is by.its other end fixed to the middle of a tense
membrane, which has atmospheric air on both sides.

A tense membrane is a much better conductor of the
vibrations of air than any other solid body bounded by
definite surfaces: and the vibrations are also communi-
cated very readily by tense membranes to solid bodies in |
contact with them. Thus, then, the membrana tympani
serves for the transmission of sound from the air to the
chain of auditory bones. Stretched tightly in its osseous
ring, it vibrates with the air in the auditory passage, as
any thin tense membrane will when the air near it is
thrown into vibrations by the sounding of a tuning-fork
or a musical string. And, from such a tense vibrating
membrane, the vibrations are communicated with great
intensity to solid bodies which touch it at any point. If,
for example, one end of a flat piece of wood be applied to
the membrane of a drum while the other end is held in
the hand, vibrations are felt distinctly when the vibrating
tuning-fork is held over the membrane without touching
it; but the wood alone, isolated from the membrane, will

only very feebly propagate the vibrations of the air to the
hand.

-

i= 2m.

— ee a en ee oe ee + eae

FUNCTIONS OF THE MIDDLE EAR. 685

The ossicula of the ear, which are represented in this
experiment by a piece of wood, are the better conductors
of the sonorous vibrations communicated to them, on
account of being isolated by an atmosphere of air, and not
continuous with the bones of the cranium; for every solid
body thus isolated by a different medium, propagates
vibrations with more intensity through its own substance
than it communicates them to the surrounding medium,
which thus prevents a dispersion of the sound; just as
the vibrations of the air in the tubes used for conducting
the voice from one apartment to another are prevented from
being dispersed by the solid walls of the tube. The
vibrations of the membrana tympani are transmitted,
therefore, by the chain of ossicula to the fenestra ovalis
and fluid of the labyrinth, their dispersion in the tympanum
being prevented by the difficulty of the transition of
vibrations from solid to gaseous bodies. The membrana
tympani being a tense, solid body, bounded by free sur-
faces, the sonorous undulations will be partially reflected
at its surfaces, so as to cause a meeting of undulations
from- opposite directions within it; it will, therefere, by
resonance, increase the intensity of the vibrations commu-
nicated to it, and the undulations, thus rendered more
intense, will act, in their turn, upon the chain of auditory
bones.

The necessity of the presence of air on. the inner side
of the membrana tympani, in order to enable it and the
ossicula auditus to fulfil the objects just described, is
obvious. Without this provision, neither would the vibra-
tions of the membrane be free, nor the chain of bones
isolated, so as to propagate the sonorous undulations with
concentration of their intensity. But while the oscilla-
tions of the membrana tympani are readily communicated
to the air in the cavity of the tympanum, those of the
solid ossicula will not be conducted away by the air, but
will be propagated to the labyrinth without being dispersed

s

686 . THE SENSE OF HEARING.

in the tympanum. Equally necessary is the communica-
tion of the air in the tympanum with the external air,
through the medium of the Eustachian tube, for the main- |
tenance of the equilibrium of pressure and temperature
between them.

The propagation of sound through the ossicula of the
tympanum to the labyrinth must be effected either by
oscillations of the bones, or by a kind of molecular vibra-
tion of their particles, or, most probably, by both these
kinds of motion.*

The long process of the malleus receives the undulations

Fig. 201. of the membrana tympani (fig. 201,
a, a) and of the air in a direction
indicated by the arrows, nearly per-
pendicular to itself. From the long
process of the malleus they are
propagated to its head (b); thence
into’ the incus (c), the long proceses
of which is parallel with the long
process of the malleus. From the
long process of the incus the undu-
lations are communicated to the
stapes (d), which is united to the
incus at right angles. The several
changes in the direction of the chain
of bones have, however, no influence on that of the undu-
lations, which -remains the same as it was in the meatus ©
externus and long process of the malleus, so that the undu-
lations are communicated by the stapes to the fenestra
ovalis in a perpendicular direction.

* Edouard Weber has shown that the existence of the membrane over
the fenestra rotunda will permit approximation and remoyal of the stapes
to and from the labyrinth. When by the stapes the membrane of the
fenestra ovalis is pressed towards the labyrinth, the membrane of the —
fenestra rotunda may, by the pressure communicated through the fluid
of the labyrinth, be pressed towards the cavity of the tympanum.

FUNCTIONS OF THE MIDDLE EAR. 687

Increasing tension of the membrana tympani diminishes
the facility of transition of sonorous undulations from the
air to it. Mr. Savart observed that the dry membrana
tympani, on the approach of a body emitting a loud sound,
rejected particles of sand strewn upon it more strongly
when lax than when very tense; and inferred, therefore,
that hearing is rendered less acute by increasing the ten-
sion of the membrana tympani. Miiller has confirmed
this by experiments with small membranes arranged so
as to imitate the membrana tympani; and it may be con-
firmed also by observations on one’s self. For the mem-
brana tympani on one’s own person may be rendered tense
at will in two ways, namely, by a strong and continued
effort of expiration or of inspiration while the mouth and
nostrils are closed. In the first case, the compressed air
is forced with a whizzing sound into the tympanum, the
membrana tympani is made tense, and immediately hear-
ing becomes indistinct. The same temporary imperfection
of hearing is produced by rendering the membrana tym-
pani tense, and convex towards the interior, by the effort
of inspiration. The imperfection of hearing, produced by
the last-mentioned method, may continue for a time even
after the mouth is open, in consequence of the previous
effort at inspiration having induced collapse of the walls
of the Eustachian tube, which prevents the restoration of
equilibrium of pressure between the air within the tym-
panum and that without: hence we have the opportunity
of observing that even our own voice is heard with less
intensity when the tension of the membrana tympani is
great.

If the pressure of the external air or atmosphere be
very great, while on account of collapse of the walls of
the Eustachian tube, the air in the interior of the tym-
panum fails to exert an equal counter-pressure, the mem-
brana tympani will of course be forced inwards, and
imperfect deafness be produced. Thus it may be explained

688 THE SENSE OF HEARING.

why, in a diving-bell, voices sound faintly. In all cases,
the effect of the increased tension of the membrana tym-
pani is not to render both grave and acute sounds equally
fainter than before. On the contrary, as observed by Dr.
Wollaston, the increased tension of the membrana tympani,
produced by exhausting the cavity of the tympanum, makes
one deaf to grave sounds only.

The principal office of the Eustachian tube, in Miiller’s
opinion, has relation to the prevention of these effects of
increased tension of the membrana tympani. Its existence
and openness will provide for the maintenance of the
equilibrium between the air within the tympanum and
the external air, so as to prevent the inordinate tension
of the membrana tympani which would be produced by
too great or too little pressure on ‘either side. While dis-
charging this office, however, it will serve to render sounds
clearer, as (Henle suggests) the apertures in violins do; to
supply the tympanum with air; and to be an outlet for
mucus: and the ill effects of its obstruction may be
referred to the hindrance of all these its offices, as well as.
of that one ascribed to it as its principal use.

The influence of the tensor tympani muscle in modifying
hearing, may also be probably explained in connection
with the regulation of the tension of the membrana tym-
pani. If, through reflex nervous action, it can be excited
to contraction by a very loud sound, just as the iris and
orbicularis palpebrarum muscle are by a very intense
light, then it is manifest that a very intense sound would,
through the action of this muscle, induce a deafening or
muffling of the ears. In favour of this supposition we
have the fact that a loud sound excites, by reflexion,
nervous action, winking of the eyelids, and, in persons of
irritable nervous system, a sudden contraction of many
muscles. |

The influence of the stapedius muscle in hearing, is —
unknown. It acts upon the stapes in such a manner as to

FUNCTIONS OF THE LABYRINTH. 689

make it rest obliquely in the fenestra ovalis, depressing
that side of it on which it acts, and elevating the other side
to the same extent. 3

When the fenestra ovalis and fenestra rotunda exist
together with a tympanum, the sound is transmitted to the
fluid of the internal ear in two ways,—namely, by solid
bodies and by membrane; by both of which conducting
media sonorous vibrations are communicated to water with
considerable intensity. The sound being conducted to the
' labyrinth by two paths, will, of course, produce so much
the stronger impression; for undulations will be thus
excited in the fluid of the labyrinth from two different
though contiguous points; and by the crossing of these
‘undulations stationary waves of increased intensity will
be produced in the fluid. Miiller’s experiments show that
the same vibrations of the air act upon the fluid of the
labyrinth with much greater intensity through the medium
of the chain of auditory bones and the fenestra ovalis
than through the medium of the air of the tympanum
and the membrane closing the fenestra rotunda: but the
cases of disease in which the ossicula have been lost with-
out loss of hearing, prove that sound may also be well
conducted through the air of the tympanum and the mem.
brane of the fenestra rotunda.

Functions of the Labyrinth.

The fluid of the labyrinth is the most general and constant
of the acoustic provisions of the labyrinth. In all forms
of organs of hearing, the sonorous vibrations affect
the auditory nerve through the medium of liquid—the
most convenient medium, on many accounts, for such a
purpose.

The function usually ascribed to the semicircular canals is
the collecting in their fluid contents, the sonorous undula-

tions from the bones of the cranium. They have probably,
YY

690 THE SENSE OF HEARING,

also, in some degree, the power of conducting sounds in
the direction of their curved cavities more easily than the
sounds are carried off by the surrounding hard parts in
the original direction of the undulations, though this con-
ducting power is in them much less perfect than in tubes
containing air.

Admitting that they have these powers, the increased
intensity of the sonorous vibrations thus attained will be
of advantage in acting on the auditory nerve where it is
expanded in the ampullee of the canals, and in the utri-
culus. Where the membranous canals are in contact with
the solid parietes of the tubes, this action must be much
more intense. But the membranous semicircular canals
must have a function independent of the surrounding hard
parts; for in the Petromyzon they are not separately
enclosed in solid substance, but lie in one common cavity
with the utriculus.

The crystalline pulverulent masses in the labyrinth would
reinforce the sonorous vibrations by their resonance, even
if they did not actually touch the membranes upon which
the nerves are expanded; but, inasmuch as these bodies
lie in contact with the membranous parts of the labyrinth,
and the vestibular nerve-fibres are imbedded in them, they
communicate to these membranes and the nerves vibratory
impulses of greater intensity than the fluid of the labyrinth
can impart. This appears to be the office of the otoconia.
Sonorous undulations in water are not perceived by the
hand itself immersed in the water, but are felt distinctly
through the medium of a rod held in the hand. The fine
hair-like prolongations from the epithelial cells of the
ampulle have, probably, the same function.

The cochlea seems to be constructed for the spreading out
of the nerve-fibres over a wide extent of surface, upon a
solid lamina which communicates with the solid walls of
the labyrinth and cranium, at the same time that it is in
contact with the fluid of the labyrinth, and which, besides

FUNCTIONS OF THE COCHLEA. 691

exposing the nerve-fibres to the influence of sonorous
undulations by two media, is itself insulated by fluid on
either side.

The connection of the lamina spiralis with the solid
walls of the labyrinth, adapts the cochlea for the percep-
tion of the sonorous undulations propagated by the solid
parts of the head and the walls of the labyrinth. The
membranous labyrinth of the vestibule and semicircular
canals is suspended free in the perilymph, and is destined
more particularly for the perception of sounds through the
medium of that fluid, whether the sonorous undulations
be imparted to the fluid through the fenestra, or by the
intervention of the cranial bones, as when sounding bodies
are brought into communication with the head or teeth.
The spiral damina on which the nervous fibres are ex-
panded in the cochlea, is, on the contrary, continuous with
the solid walls of the labyrinth, and receives directly from

them the impulses which they transmit. This is an

important advantage ; for the impulses imparted by solid
bodies, have, c@teris paribus, a greater absolute intensity
than those communicated by water. And, even when a
sound is excited in the water, the sonorous undulations
are more intense in the water near the surface of the
vessel containing it, than in other parts of the water
equally distant from the point of origin of the sound: thus
we may conclude that, ceteris paribus, the sonorous undula-
tions of solid bodies act with greater intensity than those
of water. Hence we perceive at once an important use of
the cochlea.

This is not, however, the sole office of the cochlea; the
spiral lamina, as well as the membranous labyrinth,
receives sonorous impulses through the medium of the
fluid of the labyrinth from the cavity of the vestibule, and
from the fenestra rotunda. The lamina spiralis is, indeed,
much better calculated to render the action of these undu-
lations upon the auditory nerve efficient, than the mem-

Va

692 THE SENSE OF HEARING,

branous labyrinth is; for, as a solid body insulated by a
different medium, it is capable of resonance.

The rods of Corti are probably arranged so that each is ;
set to vibrate in unison with a particular tone, and thus
strike a particular note, the sensation of which is carried
to the brain by those filaments of the auditory nerve with
which the little vibrating rod is connected.

The distinctive function therefore of those minute bodies
is, probably, to render sensible to the brain the various
musical notes and tones, one of them answering to one tone,
and one to another; while perhaps the other parts of the
organ of hearing discriminate between the intensities of
different sounds, rather than their qualities.

Sensibility of the Auditory Nerve.

Most frequently, several undulations or impulses on the
auditory nerve concur in the production of the impressions
of sound.

By the rapid succession of several impulses at unequal
intervals, a noise or rattle is produced ; from a rapid suc-
cession of several impulses af equal intervals, a musical
sound results, the height or acuteness of which increases
with the number of the impulses communicated to the ear
within a given time. A sound of definite musical value is
also produced when each one of the impulses, succeeding
another thus at regular intervals, is itself compounded of
several undulations, in such a way that, heard alone, it
would give the impression of an unmusical sound; that is
to say, by a sufficiently rapid succession of short unmusical
sounds at regular intervals, 4 musical sound is generated. .

It would appear that two impulses, which are equivalent
to four single or half vibrations, are sufficient to produce a
definite note, audible as such through the auditory nerve.
The note produced by the shocks of the teeth of a revolving
wheel, at regular intervals upon a solid body, is still heard
when the teeth of the wheel are removed in succession,

Cd ee

-DIRECTION AND DISTANCE OF SOUNDS. 693

until two only are left; the sound produced by the impulse
of these two teeth has still the same definite value in the
scale of music.

The maximum and minimum of the intervals of suc-
cessive impulses still appreciable through the auditory
nerve as determinate sounds, have been determined by
M. Savart. If their intensity is sufficiently great, sounds
are still audible which result from the succession of 48,000
half-vibrations, or 24,000 impulses in a second; and this,
‘probably, is not the extreme limit in acuteness of sounds
perceptible by the ear. For the opposite extreme, he has
‘succeeded in rendering sounds audible which were pro-
duced by only fourteen or eighteen half-vibrations, or
‘seven or eight impulses in a second; and sounds still
deeper might probably be heard, if the individual im-
pulses could be sufficiently prolonged.

By removing one or several teeth from the toothed
wheel before mentioned, M. Savart was also enabled to
satisfy himself of the fact that in the case of the auditory
nerve, as in that of the optic nerve, the sensation continues
longer than the impression which causes it; for the re-
moval of a tooth from the wheel produced no interruption of
the sound. The gradual cessation of the sensation of sound
renders it difficult, however, to determine its exact duration
beyond that of the impression of the sonorous impulses.

The power of perceiving the direction of sounds is not a
faculty of the sense of hearing itself, but is an act of the

mind judging on experience previously acquired. From
‘the modifications which the sensation of sound undergoes
-according to the direction in which the sound reaches us,
‘the mind infers the position of the sounding body. The -
-only true guide for this inference is the more intense
-action of the sound upon one than upon the other ear.

But even here there is room for much deception, by the
influence of reflexion or resonance, and by the propagation
of sound from a distance, without loss of intensity, through

694 THE SENSE OF HEARING.

curved conducting-tubes filled with air. By means of such
tubes, or of solid conductors, which convey the sonorous
vibrations from their source to a distant resonant body,
sounds may be made to appear to originate in a new
situation.

The direction of sound may also be judged of by means
of one ear only; the position of the ear and head being
varied, so that the sonorous undulations at one moment
fall upon the ear in a perpendicular direction, at another
moment obliquely. But when neither of these circum-
stances can guide us in distinguishing the- direction of
sound, as when it falls equally upon both ears, its source
being, for example, either directly in front or behind us, it
becomes impossible to determine whence the sound comes.

Ventriloquists take advantage of the difficulty with
which the direction of sound is recognised, and also the
influence of the imagination over our judgment, when they
direct their voice in a certain direction, and at the same time
pretend themselves to hear the sounds as coming from thence.

The distance of the source of sounds is not recognised by
the sense itself, but is inferred from their intensity. The
sound itself is always seated but in one place, namely, in
our ear; but it is interpreted as coming from an exterior
soniferous body. When the intensity of the voice is
modified in imitation of the effect of distance, it excites
the idea of its originating ata distance; and this is also
taken advantage of by ventriloquists.

The experiments of Savart, already referred to, prove
that the effect of the action of sonorous undulations upon
the nerve of hearing, endures somewhat longer than the
period during which the undulations are passing through
the ear. If, however, the impression of the same sound
be very long continued, or constantly repeated for a long
time, then the sensation produced may continue for a very
long time, more than twelve or twenty-four hours even,
after the original cause of the sound has ceased. This

» ed il

DIRECTION AND DISTANCE OF SOUNDS. 695

must have been experienced by every one who has travelled ,
several days continuously ; for some time after the journey,
the rattling noises are heard when the ear is not acted on
by other sounds.

We have here a proof that the perception of sound, as
sound, is not essentially connected with the existence of
undulatory pulses; and that the sensation of sound is a
state of the auditory nerve, which, though it may, be
excited by a succession of impulses, may also be produced
by other causes. Even if it be supposed that undulations
excited by the impulse are kept up in the auditory nerve
for a certain time, they must be undulations of the nervous
principle itself, which, being excited, continue until the
equilibrium is restored.

Corresponding to the double vision of the same object
with the two eyes, is the double hearing with the two
ears; and analogous to the double vision with one eye,

dependent on unequal refraction, is the double hearing of

a single sound with one ear, owing to the sound coming to
the ear through media of unequal conducting power. The
first kind of double hearing is very rare; instances of it
are recorded, however, by Sauvages and Itard. The second
kind, which depends on the unequal conducting power of
two media through which the same sound is transmitted
to the ear, may easily be experienced. If a small bell be
sounded in water, while the ears are closed by plugs, and
a solid conductor be interposed between the water and the
ear, two sounds will be heard differing in tensity and tone ;
one being conveyed to the ear through the medium of the
atmosphere, the other through the conducting-rod.

The sense of vision may vary in its degree of perfection
as regards either the faculty of adjustment to different
distances, the power of distinguishing accurately the par-
ticles of the retina affected, sensibility to light and dark-
ness, or the perception of the different shades of colour.
In the sense of hearing, there is no parallel to the faculty

696 THE SENSE OF HEARING.

by which the eye is accommodated to distance, nor to the
perception of the particular part of the nerve affected; but
just as one person sees distinctly only in a bright light,
and another only in a moderate light, so in different
individuals the sense of hearing is more perfect for sounds
of different pitch; and just as ‘a person whose vision for
the forms of objects, etc., is acute, nevertheless dis-
tinguishes colours with difficulty, and has no perception of
the harmony and disharmony of colours, so one, whose
hearing is good as far as regards the sensibility to feeble
sounds, is sometimes deficient in the power of recognising
the musical relation of sounds, and in the sense of harmony
and discord; while another individual, whose hearing is
in other respects imperfect, has these endowments. The
causes of these differences are unknown.

Subjective sounds are the result of a state of irritation or
excitement of the auditory nerve produced by other causes
than sonorous impulses. <A state of excitement of this
nerve, however induced, gives rise to the sensation of
sound. Hence the ringing and buzzing in the ears heard
by persons of irritable and exhausted nervous system, and
by patients with cerebral disease, or disease of the audi-
tory nerve itself; hence also the noise in the ears heard
for some time after a long journey in a rattling noisy
vehicle. Ritter found that electricity also excites a sound
in the ears. From the above truly subjective sound we
must distinguish those dependent, not on a state of the
auditory nerve itself merely, but on sonorous vibrations
excited in the auditory apparatus. Such are the buzzing
sounds attendant on vascular congestion of the head and
ear, or on aneurismal dilatation of the vessels, Frequently
even the simple pulsatory circulation of the blood in the
ear is heard. To the sounds of this class belong also the
snapping sound in the ear produced by a voluntary effort,
and the, buzz or hum heard during the contraction of the
palatine muscles in the act of yawning; during the forcing

SENSE OF TASTE. 697

of air into the tympanum, so as to make tense the mem-
brana tympani; and in the act of blowing the nose, as
well as during the forcible depression of the lower jaw.

Irritation or excitement of the auditory nerve is capable
of giving rise to movements in the body, and to sensations
in other organs of sense. In both cases it is probable
that the laws of reflex action, through the medium of the
brain, come into play. An intense and sudden noise
excites, in every person, closure of the eyelids, and, in ner-
vous individuals, a start of the whole body or an unpleasant
sensation, like that produced by an electric shock, through-
out the body, and, sometimes a particular feeling in the
external ear. Various sounds cause in many people a
disagreeable feeling in the teeth, or a sensation of cold
tickling through the body, and, in some people, intense
sounds are said to make the saliva collect. |

The sense of hearing may in its turn be affected by im-
pressions on many other parts of the body; especially in
diseases of the abdominal viscera, and in febrile affections.
Here, also, it is probable that the central organs of the ner-
vous system are the media through which the impression
is transmitted.

SENSE OF TASTE.

The conditions for the perception of taste are :—1, the
presence of a nerve with special endowments; 2, the
excitation of the nerves by the sapid matters, which for
this purpose must be in a state of solution. The nerves
concerned in the production of the sense of taste have been
already considered (pp. 547 and 555).

The mode of action of the substances which excite taste
probably consists in the production of a change in the
internal condition of the gustatory nerves; and, according
to the difference of the substances, an infinite variety of
changes of condition, and consequently of tastes, may be
induced. It is not, however, necessary for the manifesta-

698 THE SENSE OF TASTE.

tion of taste that sapid substances in solution should be
brought into contact with its nerves. For the nerves of
taste, like the nerves of other special senses, may have
their peculiar properties excited by various other kinds of
irritation, such as electricity and mechanical impressions.
Thus Henle observed that a small current of air directed
upon the tongue gives rise to a cool saline taste, like that
of saltpetre; and Dr. Baly has shown that a distinct sen-
sation of taste, similar to that caused by electricity, may
be produced by a smart tap applied to the papille of the
tongue. Moreover, the mechanical irritation of the fauces
and palate produces the sensation of nausea, which is
probably only a modification of taste.

The matters to be tasted must either be in solution or
be soluble in the moisture covering the tongue; hence
insoluble substances are usually tasteless, and produce
merely sensations of touch. Moreover, for the perfect
action of a sapid, as of an odorous substance, it is necessary
that the sentient surface should be moist. Hence, when
the tongue and fauces are dry, sapid substances, even in
solution, are with difficulty tasted.

The principal, but not exclusive seat of the sense of
taste is the fauces and tongue.

The tongue is a muscular organ covered by mucous
membrane; the latter resembling other mucous mem-
branes (p. 398) in essential points of structure, but con-
taining certain parts, the papille, more or less peculiar
to itself; peculiar, however, in details of structure and
arrangement, not in their nature. The tongue is beset
with numerous mucous follicles and glands. Its use in
relation to mastication and deglutition has already been
considered (p. 264).

Besides other functions, the mucous membrane of the
tongue serves as a ground-work for the ramification of
the abundant blood-vessels and nerves which the tongue
receives, and affords insertion to the extremities of the

tly oh

STRUCTURE OF THE TONGUE. 690: -

} muscular fibres of which the chief substance of the organ
| is composed.

Fig. 202.*

TT
A
iS WA
\\

he

* Fig. 202. Papillar surface of the tongue, with the fauces and tonsils
(from Sappey).—1, 1, circumvallate papille, in front of 2, the foramen
cecum ; 3, fungiform papille ; 4, filiform and conical papille ; 5, trans-
verse and oblique ruge; 6, mucous glands at the base of the tongue
and in the fauces; 7, tonsils; 8, part of the epiglottis; 9, median
glosso-epiglottidean fold, frenum epiglottidis.

700 THE SENSE OF TASTE.

The larger papille of the tongue are thickly set over the
anterior two-thirds of its upper surface, or dorswm (fig. 202),
and give to it its characteristic roughness. Their greater
prominence than those of the skin is due to their interspaces
not being filled up with epithelium, as the interspaces of
the papille of the skin are. The papille of the tongue
present several diversities of form; but three principal
varieties, differing both in seat and general characters,
may usually be distinguished, namely, the circumvallate or
calciform, the fungiform, and the jiliform papille. Essen-
tially these have all of them the same structure, that is to
say, they are all formed by a projection of the mucous
membrane, and contain special branches of blood-vessels
and nerves. In details of structure, however, they differ
considerably one from another.

All the three varieties of papille just described have
been commonly regarded as simple processes, like the
papille of the skin; but Todd and Bowman have shown
that the surface of each kind is studded by minute conical
processes of mucous membrane, which thus form secondary
papille. These secondary papille also occur over most
other parts of the tongue, not occupied by the compound
papille, and extend for some distance behind the papille
circumvallate. The mucous membrane immediately in front
of the epiglottis, is, however, free from them. They are
Fig. 203.*

* Fig. 203. Vertical section of the circumvallate papille Crom
Kélliker), *?.—A, the papille ; B, the surrounding wall; a, the epi-

thelial covering ; b, the nerves of the papilla and wall spreading to-
wards the surface ; c, the secondary papille.

aE ae Se a a A es eae

ee RT

(; .-.. =) -
=

ae

PAPILLA OF THE TONGUE. 701

commonly buried beneath the epithelium; hence they had
been previously overlooked. |

Circumvallate or Calyciform Papille.—These papillee (fig.
203), eight or ten in number, are situate in two V-shaped
lines at-the base of the tongue (1, 1, fig. 202). ‘They are
circular elevations from 5th . Fig. 204.*
to =4,th of an inch wide, each
with a central depression, and
surrounded by a circular fis-
sure, at the outside of which
again is a slightly elevated
ring, both the central elevation
and the ring being formed
of close-set simple papillee
(fig. 203).

Fungiform Papille.— The
fungiform papille (fig. 204)
are scattered chiefly over the
sides and tip, and sparingly
over the middle of the dor-
sum, of the “ongue; their
name is derived from their
being usually narrower at
their base than at their sum-
mit. They also consist of groups of simple papillee, each
of which contains in its interior a loop of capillary blood-
vessels, and a nerve-fibre.

Conical or Filiform Papille.—These, which are the most
abundant papilla, are scattered over the whole surface of
the tongue, but especially over the middle of the dorsum.

* Fig. 204. Surface and section of the fungiform papille (from
Kolliker, after Todd and Bowman).—A, the surface of a fungiform
papilla, partially denuded of its epithelium, **; y, secondary papillee ;
e, epithelium. B, section of a fungiform papilla with the blood-vessels
injected ; a, artery; v, vein; c, capillary loops of simple papille in
the neighbouring structure of the tongue; d, capillary loops of the
secondary papille ; ¢; epithelium. /

702 THE SENSE OF TASTE. »

They vary in shape somewhat, but for the most part |
are conical or filiform, and covered by a thick layer of
epidermis, which is arranged over them, either in an im-

Fig. 205. _ bricated manner, or
is prolonged from
their surface in the
form of fine stiff pro-
jections, hair-like in
appearance, and in
some instances in
structure also (fig..
205). From their
peculiar structure, it
seems likely that
these papille have
a mechanical fune-
tion, or one allied
to. that of touch,
rather than of taste ;
the latter sense being
probably seated espe-
cially in the other two
varieties of papillee, |
the cirewmvallate and
the fungiform.

The epithelium of
the tongue is of the
squamous or tesselated kind (p. 30). It covers every
part of the surface; but over the fungiform papille

* Fig. 205. Two filiform papille, one with epithelium, the other
without (from Kdélliker, after Todd and Bowman). ‘**.—p, the sub- .
stance of the papille dividing at their upper extremities into secondary
papille ; a, artery ; and v, vein, dividing into capillary loops; ¢, epi-
thelial covering, laminated between the papille, but extended into hair-
like processes J, from the extremities of the secondary papilla.

‘
j
+

of
x
»
?

i
a
4
9
‘

PAPILLE OF THE TONGUE. | —-_ 703

forms a thinner layer than elsewhere, so that these
papillee stand out more prominently than the rest. The
epithelium covering the filiform papille has been shown
by Todd and Bowman to have a singular arrangement;

being extremely dense and thick, and, as before men- .

tioned, projecting from their sides and summits in the
form of long, stiff, hair-like processes. Many of these
processes bear a close resemblance to hairs, and some
actually contain minute air-tubes. Blood-vessels and
nerves are supplied freely to the papille. The nerves in
the fungiform and circumvallate papillae form a kind of
plexus, spreading out brush-wise (fig. 203), but the exact
mode of termination of the nerve-filaments is not certainly
known.

Such, in outline, is the structure of the sensitive surface
of the tongue. But the tongue is not the only seat of the
sense of taste; for the results of experiments as well as
ordinary experience show that the soft palate and its
arches, the uvula, tonsils, and probably the upper part of
the pharynx, are endowed with taste. These parts, toge-
ther with the Lase and posterior parts of the tongue, are
supplied with branches of the glosso-pharyngeal nerve, and
evidence has been already adduced (p. 556 et seq.) that the
sense of taste is conferred upon them by this nerve.

In most, though not in all persons, the. anterior part of
the tongue, especially the edges and tip, are endowed with
the sense of taste. The middle of the dorsum is only
feebly endowed with this sense, probably because of the
density and thickness of the epithelium covering the fili-
form papillee of this part of the tongue, which will prevent

-the sapid substances from penetrating to their sensitive

parts. The gustatory property of the anterior part of the
tongue is due, as already said (p. 547), to the lingual
branch of the fifth nerve.

Besides the sense of taste, the tongue, by means also of
its papille, is endued, especially at its sides and tip, with

-

704 THE SENSE OF TOUCH,

a very delicate and accurate sense of touch, which renders
it sensible of the impressions of heat and cold, pain, and
mechanical pressure, and consequently of the form of
surfaces. The tongue may lose its common sensibility,
and still retain the sense of taste, and vice versé. This fact
renders it probable that, although the senses of taste and
of touch may be exercised by the same papille supplied
by the same nerves, yet the nervous conductors for these
two different sensations are distinct, just as the nerves for
smell and common sensibility in the nostrils are distinct ;
and it is quite conceivable that the same nervous trunk
may contain fibres differing essentially in their specific
properties. Facts already detailed (p. 547) seem to prove
that the lingual branch of the fifth nerve is the seat of
sensations of taste in the anterior part of the tongue: and
it is also certain, from the marked manifestations of pain
to which its division in animals gives rise, that it is like-
wise a nerve of common sensibility. The glosso-pharyngeal
also seems to contain fibres both of common sensation and
of the special sense of taste.

The concurrence of common and special sensibility in
the same part makes it sometimes difficult to determine
whether the impression produced by a substance is per-
ceived through the ordinary sensitive fibres, or through
those of the sense of taste. In many cases, indeed, it is
probable that both sets of nerve-fibres are concerned, as
when irritating acrid substances are introduced into the ,
mouth.

The impressions on the mind leading to the perception
of taste seem to result, as already said, from certain
changes in the internal condition of the nerves produced
by the contact of sapid substances with the papille in
which the fibres of these nerves are distributed. This
explanation, obscure though it be, may account generally
for the sense; but the variations of taste produced by
different substances are as yet inexplicable. .In the case

THE SENSE OF TASTE. 705

of hearing, we know that sounds differ from one another -
according to the differences in the number of undulations
producing them; and in the case of vision, it is reasonably
inferred that different colours result from differences in
the number of undulations, or in the rate of transit, of the
principle of light. But, in the cases of taste and smell, no
such probable explanation has yet been offered. It would
appear, indeed, from the experiments of Horn, that while
some substances taste alike in all regions of the tongue’s
surface, others excite different tastes, according as they are
applied to different papille of the tongue. This observa-
tion, if confirmed, would seem to show that, in some cases
at least, different fibres are capable of receiving different
impressions from the same sapid substance.

Much of the perfection of the sense of taste is often due
to the sapid substances being also odorous, and exciting
the simultaneous action of the sense of smell. This is
shown by the imperfection of the taste of such substances
when their action on the olfactory nerves is prevented by
closing the nostrils. Many fine wines lose much of their
apparent exceilence if the nostrils are held close while they
are drunk.

Very distinct sensations of taste are frequently left after
the substances which excited them have ceased to act on
the nerve; and such sensations often endure for a long
time, and modify the taste of other substances applied to
the tongue afterwards. Thus, the taste of sweet substances
spoils the flavour of wine, the taste of cheese improves it.
There appears, therefore, to exist the same relation between
tastes as between colours, of which those that are opposed
or complementary render each other more vivid, though
no general principles governing this relation have been
discovered in the case of tastes. In the art of cooking,
~ however, attention has at all times been paid to the con-
sonance or harmony of flavours in their combination or

order of succession, just as in painting and music the
ZZ

706 . THE SENSE OF TOUCH.

fundamental principles of harmony have been employed
empirically while the theoretical laws were unknown.

Frequent and continued repetitions of the same taste
render the perception of it less, and less distinct, in the
same way that a colour becomes more and more dull and-
indistinct the longer the eye is fixed upon it. Thus, after
frequently tasting first one and then the other of two kinds
of wine, it becomes impossible to discriminate between
them. . .
The simple contact of a sapid substance with the sur-
face of the gustatory organ seldom gives rise to a distinct
sensation of taste; it needs to be diffused over the surface,
and brought into intimate contact with the sensitive parts
by compression, friction, and motion between the tongue
and palate.

The sense of taste seems capable of being excited also
by internal causes, such as changes in the conditions of
the nerves or nerve-centres, produced by congestion or
other causes, which excite subjective sensations in the
other organs of sense. But little is known of the sub-
jective sensations of taste; for it is difficult to distin-
guish the phenomena from the effects of external causes,
such as changes in the nature of the secretions of the
mouth.

SENSE OF TOUCH.

The sense of touch is not confined to particular parts of
the body of small extent, like the other senses; on the
contrary, all parts capable of perceiving the presence of
a stimulus by ordinary sensation are, in certain degrees,
the seat of this sense; for touch is simply a modification
or exaltation of common sensation or sensibility. The
nerves on which the sense of touch depends are, therefore,
the same as those which confer ordinary sensation on the
different parts of the body, viz., those derived from the
posterior roots of the nerves of the spinal cord, and the
sensitive cerebral nerves, |

*

THE SENSE OF TOUCH. 707

But, although all parts of the body supplied with sensi-
tive nerves are thus, in some degree, organs of touch, yet
the sense is exercised in perfection only in those parts the
sensibility of which is extremely delicate, e.g., the skin,
~ the tongue, and the lips, which are provided with abun-
dant papille. (See chapter on Sxry, and section on
TASTE. )

The sensations of the common sensitive nerves have as
peculiar a character as those of any other organ of sense.
The sense of touch renders us conscious of the presence of
a stimulus, from the slightest to the most intense degree
of its action, neither by sound, nor by light, nor by colour,
but by that indescribable something which we call feeling, |
or common sensation. The modifications of this sense
often depend on the extent of the parts affected. The
sensation of pricking, for example, informs us that the
sensitive particles are intensely affected in a small extent;
the sensation of pressure indicates a slighter affection of
the parts in a greater extent, and to a greater depth. It
is by the depth to which the parts are affected that the
feeling of pressure is distinguished from that of mere
contact. Schiff and Brown-Séquard are of opinion that
common sensibility and tactile sensibility manifest them-
selves to the individual by the aid of different sets of fibres.
Dr. Sieveking has arrived at the same conclusion from
pathological observation.

By the sense of touch the mind is made acquainted with
the size, form, and other external characters of bodies.
And in order that these characters may be easily ascer-
tained, the sense of touch is especially developed in those
parts which can be readily moved over the surface of —
bodies. Touch, in its more limited sense, or the act
of examining a body by the touch, consists merely ina
voluntary employment of this sense combined with move-
ment, and stands in the same relation to the sense of

touch, or common sensibility, generally, as the act of seek-
Z2Z2

708 THE SENSE OF TOUCH.

ing, following, or examining odours, does to the sense of
smell. Every sensitive part of the body which can, by
means of movement, be brought into different relations of
contact with external bodies, is an organ of ‘‘ touch.” No
one part, consequently, has exclusively this function. The
hand, however, is best adapted for it, by reason of its.
peculiarities of structure,—namely, its capability of pro-
nation and supination, which enables it, by the movement
of rotation, to examine the whole circumference of a body;.
the power it possesses of opposing the thumb to the rest.
of the hand; and the relative mobility of the fingers. —
Besides—the hand, and especially. the fingers, are abun-
dantly endowed with papille and touch-corpuscles (pp. 424,
425) which are specially necessary for the perfect employ-
ment of this sense.

In forming a conception of the figure and extent of a
surface, the mind multiplies the size of the hand or fingers
used in the inquiry by the number of times which it is
contained in the surface traversed; and by repeating this
process with regard to the different dimensions of a solid.
body, acquires a notion of its cubical extent.

The perfection of the sense of touch on different parts
of the surface is proportioned to the power which such
parts possess of distinguishing and isolating the sensa-
tions produced by two points placed close together. This
power depends, at least in part, on the number of primitive
nerve-fibres distributed to the part; for the fewer the
primitive fibres which an organ receives, the more likely
is it that several impressions on different contiguous points
will act on only one nervous fibre, and hence be con-
founded, and perhaps produce but one sensation. Ex-
periments to determine the tactile properties of different
parts of the skin, as measured by this power of distin-
guishing distances, were made by E. H. Weber. One
experiment consisted in touching the skin, while the eyes
were closed, with the points of a pair of compasses sheathed

a

THE SENSE OF TOUCH. 709

with cork, and in ascertaining how close the points of the
compasses might be brought to each other, and still be
felt as two bodies. He examined in this manner nearly
every part of the surface of the body, and has given tables
showing the relative degrees of sensibility of different
parts. Experiments of a similar kind have been per-
formed also by Valentin: and, among the numerous
results obtained by both these investigators, it appears
that the extremity of the third finger, and the point of the
tongue are the parts most sensitive: a distance of as little
as half a line being here distinguished. Next in sensitive-
ness to these is the mucous surface of the lips, which can
perceive the two points of the compass when separated to
the distance of about-a line and a half: on the dorsum of
the tongue they require to be separated two lines. The
parts in which the sense of touch is least acute are the
neck, the middle of the back, the middle of the arm, and
the middle of the thigh, on which the points of the com.
pass have to be separated to the distance of thirty lines to
be perceived as distinct points (Weber). Other parts of
the body possess various degrees of sensibility intermediate
between the above extremes.

A sensation in a part endowed with touch appears to
the mind to be, c@teris paribus, more intense when it is
excited in a large extent of surface than when it is con-
fined to a small space. ‘The temperature of water into
which he dipped his whole hand, appeared to Weber to be
higher than that of water of really higher temperature,
in which he immersed only one finger of the other hand.
Similar observations may be made by persons bathing in
warm or cold water.

Part of the ideas which we obtain of the conditions of
external bodies is derived through the peculiar sensibility
with which muscles are endowed—the sensibility by which
we are made acquainted with their position, and the degree
of their contraction. By this sensation, we are enabled to

710 THE SENSE OF TOUCH.

estimate the degree of force exerted in resisting pressure
or in raising weights. The estimate of weight by mus-
cular effort is more accurate than that by pressure on the
skin, according to Weber, who states that by the former
a difference between two weights may be detected when
one is only one-twentieth or one-fifteenth less than the
other. It is not the absolute, but the relative, amount of
the difference of weight which we have thus the faculty
of perceiving.

It is not, however, certain, that our idea of the amount
of muscular force used is derived solely from sensation in
the muscles. We have the power of estimating very
accurately beforehand, and of regulating, the amount of
nervous influence necessary for the production of a certain
degree of movement. When we raise a vessel, with the
contents of which we are not acquainted, the force we
employ is determined by the idea we have conceived of its
weight. If it should happen to contain some very heavy
substance, as quicksilver, we shall probably let it fall;
the amount of muscular action, or of nervous energy,
which we had exerted, being insufficient. The same thing
occurs sometimes to a person descending stairs in the
dark; he makes the movement for the descent of a step
which does not exist. It is possible that in the same way
the idea of weight and pressure in raising bodies, or in
~ resisting forces, may in part arise from a consciousness of
the amount of nervous energy transmitted from the brain
rather than from a sensation in the muscles themselves.
The mental conviction of the inability longer to support a
weight must also be distinguished from the actual sensa-
tion of fatigue in the muscles. ©

So, with regard to the ideas derived from sensation of
touch combined with movements, it is doubtful how far
the consciousness of the extent of muscular movement is.
obtained from sensations in the muscles themselves. The
sensation of movement attending the motions of the hand

Oi ta

/

THE SENSE OF TOUCH. 711

is very slight; and persons who do not know that the
action of particular muscles is necessary for the production”
of given movements, do not suspect that the movement of
the fingers, for example, depends on an action in the fore-
arm. The mind has, nevertheless, a very definite know-
ledge of the changes of position produced by movements ;
and it is on this that the ideas which it conceives of
the extension and form of a body are in great measure
founded.

In order that an impression made on a sensitive surface
may be perceived, it is necessary that there should exist
a reciprocal influence between the mind and the sense of
touch; for, if the mind does not thus co-operate, the
organic conditions for the sensation may be fulfilled, but
it remains unperceived. Moreover, the distinctness and
intensity of a sensation in the nerves of touch depend,
in great measure, on the degree in which the mind co-

operates for its perception. A painful sensation becomes

more intolerable the more the attention is directed to it:
thus, a sensation in itself inconsiderable, as an itching in
a very smali spot of the skin, may be rendered very
troublesome and enduring.

As every sensation is attended with an idea, and leaves
behind it an idea in the mind which can be reproduced at
will, we are enabled to compare the idea of a past sensation
with another sensation really present. Thus we can com-
pare the weight of one body with another which we had
previously felt, of which the idea is retained in our mind.
Weber was indeed able to distinguish in this manner
between temperatures, experienced one after the other,
better than between temperatures to which the two hands
were simultaneously subjected. This power of comparing
present with past sensations diminishes, however, in pro-
portion to the time which has elapsed between them.

The after-sensations left by impressions on nerves of com-
mon sensibility or touch are very vivid and durable. As

712 THE SENSE OF TOUCH.

long as the condition inte which the stimulus has thrown
the organ endures, the sensation also remains, though the
exciting cause should have long ceased to act. Both pain-
ful and pleasurable sensations afford many examples of
this fact. . .

The law of contrast, which we have shown modifies the —
sensations of vision, prevails here also. After the body
has been exposed to a warm atmosphere, a degree of
temperature a very little lower, which would under other
circumstances appear warm, produces the sensation of cold ;
and a sudden change to the extent of a few degrees from
a cold temperature to one less severe, will produce the
- sensation of warmth. Heat and cold are, therefore, rela-
tive terms; for a particular state of the sentient organs
causes what would otherwise be warmth to appear cold.
So, also a diminution in the intensity of a long-continued
pain gives pleasure, even though the degree of pain that
remains would in the healthy state have seemed intoler-
able.-

Subjective sensations, or sensations dependent on internal
causes, are in no sense more frequent than in the sense of
touch. All the sensations of pleasure and pain, of heat
and cold, of lightness and weight, of fatigue, etc., may be
produced by internal causes. Neuralgic pains, the sensa-
tion of rigor, formication or the creeping of ants, and the
states of the sexual organs occurring during sleep, afford
striking examples of subjective sensations.

The mind, also, has a remarkable power of exciting
sensations in the nerves of common sensibility; just as the
thought of the nauseous excites sometimes the sensation of
nausea, so the idea of pain gives rise to the actual sensa-
tion of pain in a part predisposed to it. The thought of
anything horrid excites the sensation of shuddering; the
feelings of eager expectation, of pathetic emotion, of.
enthusiasm, excite in some persons a sensation of ‘‘ con-
centration”’ at the top of the head, and of cold trickling

GENERATION AND DEVELOPMENT. F¥3

through the body; fright causes sensations to be felt in
many parts of the body; and even the thought of tickling
excites that sensation in individuals very susceptible of it,
when they are threatened with it by the movements of
another person. These sensations from internal causes are
most frequent in persons of excitable nervous systems, such
as the hypochondriacal and the hysterical, of whom it is
usual to say that their pains are imaginary. If by this is
meant that their pains exist in their imagination merely,
it is certainly quite incorrect. Pain is neyer imaginary
in this sense; but is as truly pain when arising from
internal as from external causes; the idea of pain only
can be unattended with. sensation, but of the mere idea
no one will complain. Still, it is quite certain that the
imagination can render pain that already exists more in-
tense and can excite it when there is a disposition to it.

CHAPTER XX.
GENERATION AND DEVELOPMENT.

Tne several organs and functions-of the human body
which have been considered in the previous chapters, have
relation to the individual being. We have now to con-
sider those organs and functions which are destined for
the propagation of the species. These comprise the several
provisions made for the formation, impregnation, and
development of the ovum, from which the embryo or foetus
is produced and gradually perfected into a fully-formed
human. being. |

The organs concerned in effecting these objects are
named the generative organs, or sexual apparatus, since
part belong to the male and part to the female sex.

gta GENERATION AN D DEVELOPMENT.

Generative Organs of the Female.

The female organs of generation consist of two Ovaries,
whose function is the formation of ova; of a Lallopian
tube, or oviduct, connected with each ovary, for the pur-
pose of conducting the ovum from the ovary to the uterus
or cavity in which, if impregnated, it is retained until the
embryo is fully developed, and fitted to maintain its
existence, independently of internal connection with the
parent; and, lastly, of a canal, or vagina, with its ap-
pendages, tor the reception of the male generative organ

Fig. 206*

* Fig. 206. Diagrammatic view of the uterus and its appendages,
as seen from behind (from Quain). 4.—The uterus and upper part
of the vagina have been laid open by removing the posterior wall; the
Fallopian tube, round ligament, and ovarian ligament have been cut
short, and the broad ligament removed on the left side; «, the upper
part of the uterus ; c, the cervix opposite the os internum ; the triangular
shape of the uterine cavity is shown, and the dilatation of the cervical
cavity with the ruge termed arbor vite; v, upper part of the vagina ;
od, Fallopian tube or oviduct ; the narrow communication of its cavity —
with that of the cornu of the uterus on each side is seen; 7, round
ligament ; Jo, ligament of the ovary ; 0, ovary; 7, wide outer part of —
the right Fallopian tube ; fi, its fimbriated extremity ; po, parovarittm ;
h, one of the hydatids frequently found connected with the broad
ligament.

FEMALE ORGANS OF GENERATION. 715

in the act of copulation, and for the subsequent discharge
of the foetus.

The ovaries are two oval compressed bodies, situated in
the cavity of the pelvis, one on each side, enclosed in the
folds of the broad ligament. Every ovary is attached to
the uterus by a narrow fibrous cord (the ligament of the
ovary), and, more slightly, to the Fallopian tube by one
of the fimbriee, into which the walls of the extremity of
the tube expand.

The ovary is enveloped by a capsule of dense fibro-
cellular tissue, which again is surrounded by peritoneum.
The internal structure of the organ consists of a peculiar
soft fibrous tissue, or stroma, abundantly supplied with
blood-vessels, and having embedded in it, in various stages
of development, numerous minute follicles or vesicles, the
Graajian vesicles, or sacculi, containing the ova (fig. 207).
A further account of the Graafian vesicles. and of their
contained ova will be presently given.

The Fallopian tubes are about four inches in length, and
extend between the ovaries and the upper angles of the
uterus. At,the point of attachment to the uterus, the
Fallopian tube is very narrow; but in its course to the
ovary it increases to about a line and a half in thickness ;
at its distal extremity, which is free and floating, it bears
a number of fimbri@, one of which, longer than the rest, is
attached to the ovary. The canal by which each Fallopian
tube is traversed is narrow, especially at its point of
entrance into the uterus, at which it will scarcely admit a
bristle; its other extremity is wider, and opens into the
cavity of the abdomen, surrounded by the zone of fimbrie.
Externally, the Fallopian tube is invested with perito-
neum ; internally, its canal is lined with mucous mem-
brane, covered with ciliary epithelium (p. 33): between
the peritoneal and mucous coats, the walls are composed,
like those of the uterus, of fibrous tissue and organic
muscular fibres (pp. 581-3).

‘

716 GENERATION AND DEVELOPMENT.

The uterus (u, ¢, fig. 206) is a somewhat pyriform, fibrous
organ, with a central cavity lined with mucous membrane.
In the unimpregnated state it is about three inches in
length, two in breadth at its upper part, or fundus, but atits

Fig. 207.*

lower pointed part or neck, only about half an inch. The
part between the fundus and neck is termed the body of
the uterus: it is about an inch in thickness. The walls
of the: organ are composed of dense fibro-cellular tissue,
with which are intermingled fibres of organic muscle: in
the impregnated state the latter are much developed and
increased in number. The cavity of the uterus corresponds

* Fig. 207. View of a section of the prepared ovary of the cat (from
‘Schrén). $.—1, outer covering and free border of the ovary ; 1’, attached
border ; 2, the ovarian stroma, presenting a fibrous and vascular structure ;
3, granular substance lying external to the fibrous stroma ; 4, blood-
vessels ; 5, ovigerms in their earliest stages occupying a part of the
granular layer near the surface; 6, ovigerms which have begun to
enlarge and to pass more deeply into the ovary; 7, ovigerms round
which the Graafian follicle and tunica granulosa are now formed, and
which have passed somewhat deeper into the ovary and are surrounded
by the fibrous stroma; 8, more advanced Graafian follicle with the
ovum imbedded in the layer of cells constituting the proligerous dise ;
9, the most advanced follicle containing the ovum, ete. ; 9’, a follicle
from which the ovum has accidentally escaped ; 10, corpus luteum.

THE VAGINA. 717

in form to that of the organ itself: it is very small in the
unimpregnated state; the sides of its mucous surface being
almost in contact, and probably only separated from each
other by mucus. Into its upper part, at each side, opens
the canal of the corresponding Fallopian tube: below, it
communicates with the vagina bya fissure-like opening in
its neck, the os uteri, the margins of which are distin-
guished into two lips, dn anterior and posterior. In the
mucous membrane of the cervix are found several mucous
follicles, termed ovula or glandule Nabothi: they pro-
bably form the jelly-like substance by which the os uteri is
usually found closed.

The vagina is a membranous canal, six or eight inches
long, extending obliquely downwards and forwards from
the neck of the uterus, which it embraces, to the external
organs of generation. It is lined with mucous membrane,
which in the ordinary contracted state of the canal, is
thrown into transverse folds. External to the mucous
membrane, the walls of the vagina are constructed of
fibro-cellular tissue, within which, especially around the
lower part of tae tube, is a layer of erectile tissue. The
lower extremity of the vagina is embraced by an orbicular
muscle, the constrictor vaginz; its external orifice, in the ~
virgin, is partially closed by a fold or ring of mucous
membrane, termed the hymen. The external organs of
generation consist of the clitoris, a small elongated body,
situated above and in the middle line, and constructed,
like the male penis, of two erectile corpora cavernosa, but
unlike it, without a corpus spongiosum, and not perforated
by the urethra; of two folds of mucous membrane, termed
labia interna, or nymphe; and, in front of these, of two
other folds, the labia externa, or pudenda, formed of the
external integument, and lined internally by mucous mem-
brane. Between the nymphe and beneath the clitoris is an
angular space, termed the vestibule, at the centre of whose
base is the orifice of the meatus urinarius. Numerous

718 GENERATION AND DEVELOPMENT.

mucous follicles are scattered beneath the mucous mem-—
brane composing these parts of the external organs of

generation ; and at the side of the fore part of the vagina,

are two larger lobulated glands, named vulvo-vaginal, or

Duverney’s glands, which are analogous to Cowper’s glands

in the male.

Having given this general outline of the several parts
which, in the female, contribute to the reproduction of the
species, it will now be necessary to examine successively
the formation, discharge, impregnation, and development
of the ovum, to which these several parts are subservient.

Unimpregnated Ovum.

If the structure and formation of the human ovary be
examined at any period between early infancy and ad-
vanced age, but especially during that period of life in
which the power of conception exists, it will be found to
contain, on an average, from fifteen to twenty small vesicles
or membranous sacs of various sizes; these have been al-
ready alluded to as the follicles or vesicles of De Graaf, the
anatomist who first accurately described them; they are
also sometimes called ovisacs. At their first formation, the —
Graafian vesicles, according to Schrén, are near the sur-
face of the stroma of the ovary, but subsequently become
more deeply placed; and again, as they increase in size,
make their way towards the surface. When mature, they
form little prominences on the exterior of the ovary,
covered only by the peritoneum. Lach follicle has an
external membranous envelope, composed of fine fibro-
cellular tissue, and connected with the surrounding stroma
of the ovary by networks of blood-vessels (fig. 208). This
envelope or tunic is lined with a layer of nucleated cells,
forming a kind of epithelium or internal tunic, and named
membrana granulosa. The cavity of the follicle is filled with
an albuminous fluid in which microscopic granules float ;
and it contains also the ovwm or ovule.

THE UNIMPREGNATED OVUM. 719

The ovum is a minute spherical body situated, in
immature follicles, near the centre; but in those nearer
maturity, in contact with the
membrana granulosa at that
part of the follicle which
forms a prominence on the
surface of the ovary. The
cells of the membrana granu-
losa are at that point more
numerous than elsewhere,
and are heaped around the
ovum, forming a kind of granular zone, the discus proliyerus
(fig. 208). ;

In order to examine an ovum, one of the Graafian
vesicles, it matters not whether it be of small size or
arrived at maturity, should be pricked, and the contained
fluid received upon a piece of glass. The ovum then, being
found in the midst of the fluid by means of a simple lens,
may be further examined with higher microscopic powers.
Owing to its globular form, ‘however, its structure cannot
be seen until it is subjected to gentle pressure. |

The human ovum is extremely small, measuring, accord-
ing to Bischoff, from 5}, to 34, of an inch. Its external
investment is a transparent membrane, about 5!,, of an
inch in thickness, which under the microscope, appears ag
a bright ring (fig. 209), bounded externally and internally
by a dark outline : it is called the zona pellucida, or vitelline
membrane. It adheres externally to the heap of cells con
stituting the discus proligerus.

Within this transparent investment or zona pellucida,

Fig. 208. *

* Fig. 208. Section of the Graafian vesicle of a Mammal, after Von
Baer. 1. Stroma of the ovary with blood-vessels. 2, Peritoneum.
3, and 4. Layers of the external coat of the Graafian vesicle. 5. Mem-
brana granulosa. 6. Fluid of the Graafian vesicle. 7. Granular zone,
or discus proligerus, containing the ovum (8).

720 GENERATION AND DEVELOPMENT.

and usually in close contact with it, lies the yolk or vitellus
which is composed of granules and globules of various
sizes, imbeded in a more or less fluid substance. The
smaller granules, which are the more numerous, resemble
in their appearance, as well as
their constant motion, pigment-
granules. The larger granules or
globules which have the aspect of
fat-globules, are’'in greatest num-
ber at the periphery of the velk.
The number of the granules is,
according to Bischoff, greatest in
the ova of carnivorous animals. In
- the human ovum their quantity is comparatively small.

In the substance of the yolk is embedded the germinal
vesicle, or vesicula germinativa (figs. 209, 210). This
vesicle is of greatest relative size in the smallest ova,
and is in them surrounded closely by the yelk, nearly in
the centre of which it lies. During the development of
the ovum, the germinal vesicle increases in size much less
rapidly than the yelk, and comes to be placed near to its
surface. Its size in the human ovum has not yet been ascer-
tained, owing to the difficulty of isolating it; but it is
probably about 4, of an inch in diameter. It consists of
a fine, transparent, structureless membrane, containing a
clear, watery fluid, in which are sometimes a few granules;
and at that part of the periphery of the germinal vesicle
which is nearest to the periphery of the yelk is situated
the germinal spot (macula germinativa), a finely granulated
substance, of a yellowish colour, strongly refracting the
rays of light, and measuring, in the Mammalia generally,
from 3755 to s_os Of an inch (Wagner).

* Fig. 209. Ovum of the sow, after Barry. 1. Germinal spot. 2.
Germinal yesicle. 3. Yelk. 4. Zonapellucida. 5. Discus proligerus.
6. Adherent granules or cells.

DEVELOPMENT OF OVUM. 721

Such are the parts of which the Graafian follicle and
its contents, including the ovum, are composed. The
diagram (fig. 210) represents them in their relative posi-
tions when mature. With regard to the mode and order
of development of these parts there is considerable un-—
certainty; but it seems most likely that the ovum is
formed before the Graafian vesicle or ovisac.

Fig. 210.*

With regard to the parts of the ovwm first formed, it
appears certain that the formation of the germinal vesicle
precedes that of the yelk and zona pellucida, or vitelline
membrane. Whether the germinal spot is formed first,
and the germinal vesicle afterwards developed around it,
cannot be decided in the case of vertebrate animals; but
the observations of Kélliker and Bagge on the develop-
ment of the ova of intestinal worms show that in these
animals, the first step in the process is the production of
round bodies resembling the germinal spots of ova, the

* Fig. 210. Diagram of a Graafian vesicle, containing an ovum. I.
Stroma or tissue of the ovary. 2 and 3. External and internal tunics
of the Graafian vesicle. 4. Cavity of the vesicle. 5. Thick tunic of the
ovum or yelk sac. 6, The yelk. 7. The germinal vesicle. 8. The
germinal spot.

3 A

722 GENERATION AND DEVELOPMENT.

germinal vesicles being subsequently developed around
these in the form of transparent membranous cells.

The more important changes that take place in the
ovum next to the formation of these its essential com-
ponent parts, consist in alterations of the size and position
of these parts with relation to each other, and of the ovum
itself with relation to the Graafian vesicle, and in the more
complete elaboration of the yelk. The earlier the stage of
development the larger is the germinal vesicle in rela-
tion to the whole ovum, and of the ovum in relation to
the Graafian vesicle. For, as the ovum becomes mature,
although all these parts increase in size, the Graafian
vesicle enlarges most, and the germinal vesicle least.
Changes take place also in the position of the parts.
The ovum at first occupies the centre of the Graafian
vesicle, but subsequently is removed to its periphery.
The germinal vesidle, too, which in young ova is in the
centre of the yelk, is in mature ova found at the peri-
phery.

The change of position of the ovum, from the centre to
the periphery of the Graafian vesicle, is possibly connected
with the. formation of the membrana granulosa which lines
the vesicle. For, according to Valentin, at a very early
period, the contents of the vesicle between its wall and the
ovum are almost wholly formed of granules; but in the
process of growth a clear fluid collects in the centre of the
vesicle, and the granules, which from the first have a
regular arrangement, are pushed outwards, and form the
membrana granulosa. Now, as the mature ovum lies em-
bedded in a thickened portion of the membrana granulosa, -
it is possible that when the elementary parts of this mem-
brane are pushed outwards, in the way just described, the ©
ovum is carried with them from the centre to the periphery
of the follicle. While the changes here described take place, —
the zona pellucida increases in thickness.

ne

DISCHARGE OF THE OVUM. 723

According to Bischoff, the number of the granules of
the yelk is greater the more mature the ovum, conse-
quently the yelk is more opaque in the mature, and more
transparent in the-immature ova. The matter in which the
granules are contained is fluid in the immature ova of all
animals; in some it remains so; but in others, as the
human ovum, it subsequently becomes a consistent gela-
tinous substance.

From the earliest infancy, and preeee the whole fruit-
ful period of life, there appears to be a constant formation,
development, and maturation of Graafian vesicles, with

their contained ova. Until the period of puberty, however,

the process is comparatively inactive ; for, previous to this
period, the ovaries are small and pale, the Graafian vesicles
in them are very minute, few in number, and probably
mever attain full development, but soon shrivel and dis-

appear, instead of bursting, as matured follicles do; the
‘contained ova are also incapable of being impregnated.
But, coincident with the other changes which occur in the
body at the time of puberty, the ovaries enlarge, and be-
ome very vascular, the formation of Graafian vesicles is
more abundant, the size and degree of development attained

by them are greater, and the ova are capable of being
fecundated.

Discharge of the Ovum.

_ In the process of development of individual vesicles, it
has been already observed, that as each increases in size, it
gradually approaches the surface of the ovary, and when
fully ripe or mature, forms a little projection on the exterior.
Coincident with the increase of size, caused by the augmen-
tation of its liquid contents, the external envelope of the
distended vesicle becomes very thin and eventually bursts.

By this means, the ovum and fluid contents of the Graafian
3A 2

724 GENERATION AND DEVELOPMENT.

, vesicle are liberated, and escape on the exterior of the
ovary, whence they pass into the Fallopian tube, the fim-
briated processes of the extremity of which are supposed.
coincidentally to grasp the ovary, while the aperture of the.
tube is applied to the part corresponding to the matured
and bursting vesicle.

In animals whose capability of being impregnated occurs.
at regular periods, as in the human subject, and most _
Mammalia, the Graafian vesicles and their contained ova |
appear to arrive at maturity, and the latter to be discharged
at such periods only. But in other animals, e.g., the
common fowl, the formation, maturation, and discharge of
ova appear to take place almost constantly. '

It has long been known, that in the so-called oviparous
animals, the separation of ova from the ovary may take
place independently of impregnation by the male, or even ~
of sexual union. And it is now established that a like
maturation and discharge of ova, independently of coition,
occurs in Mammalia, the periods at which the matured oya
are separated from the ovaries and received into the

. Fallopian tubes being indicated in the lower Mammalia,
by the phenomena of heat or rut: in the human female by |

| the phenomena of menstruation. Sexual desire manifests.
itself in the human female to a greater degree at these
periods, and in the female of mammiferous animals at no
other time. If the union -of the sexes take place, the
ovum may be fecundated, and if no union occur it
perishes.

That this maturation and discharge occur periodically,
and only during the phenomena of heat in the lower Mam-
malia, is made probable by the facts that, in all instances
in which Graafian vesicles have been found presenting
the appearance of recent rupture, the animals were at the
time, or had recently been, in heat; that on the other _
hand, there is no authentic and detailed account of

- PERIODICAL DISCHARGE OF OVA. 725

Graafian vesicles being found ruptured in the intervals of
the periods of heat; and that female animals do not admit
the males, and never become impregnated, except at those
periods.

Many circumstances make it probable that the human
female is subject, in these respects, to the same law as the
females of other mammiferous animals; namely, that ‘in
her as in them, ova are matured and discharged from the
ovary independent of sexual, union, and that this matura-
tion and discharge occur periodically, at the epochs of
menstruation. Thus Graafian vesicles recently ruptured
have been frequently seen in ovaries of virgins or women
who could not have been recently impregnated, and
although it is true that the ova discharged under these

circumstances have rarely been discovered in the Fallopian

tube,* partly on account of their minute size, and partly
because the search has seldom been prosecuted with much
care, yet analogy forbids us to doubt that in the human
female, as in the domestic quadrupeds, the result and
purpose of the rupture of the follicles is the discharge of
the ova.

The evidence of the periodical discharge of ova at the
epochs of menstruation is first, that nearly all authors who
have touched on the point, agree that no traces of follicles
having burst are ever seen in the ovaries before puberty
or the first menstruation; secondly, that in all cases in
which ovarian follicles have been found burst, indepen-
dently of sexual intercourse, the women were at the time
menstruating, or had very recently passed through the
menstrual state; thirdly, that although conception is not
confined to the periods of menstruation, yet it is more
likely to occur within a few days after the cessation of the

* See, however, the record of two such cases by Dr. Letheby, in the
Philosophical Transactions, 1851.

4

726 GENERATION AND DEVELOPMENT.

menstrual flux than at other times; and, lastly, that
the ovaries of the human female become turgid and vas-
Cular at the menstrual periods, as those of animals do at.
the time of heat. |

From what has been said, it may, therefore, be concluded
that the two states, heat and menstruation, are analogous,
and that the essential accompaniment of both, is the matu-
ration and extrusion of ova. In both there is a state of
active congestion of the sexual organs, sympathizing with
the ovaries at the time of the highest degree of develop-
ment of the Graafian vesicles; and in both, the crisis
of this state of congestion is attended by a discharge of
blood or mucus, or both, from the external organs of gene-
ration. |
The occurrence of a menstrual discharge is one of the
most prominent indications of the commencement of
puberty in the female sex; though its absence even for
several years is not necessarily attended with arrest of the
other characters of this period of life, or with inaptness.
for sexual union, or incapability of impregnation. The
average time of its first appearance in females of this
country and others of about the same latitude, is from
fourteen to fifteen; but it is much influenced by the kind
of life to which girls are subjected, being accelerated by _
habits of luxury and indolence, and retarded by contrary
conditions. On the whole, its appearance is earlier in
persons dwelling in‘ warm climes than in those inhabiting
colder latitudes; though the extensive investigations of
Mr. Roberton show that the influence of temperature on_
the development of puberty has been exaggerated. Much
of the influence attributed to climate appears due to the
custom prevalent in many hot countries, as in Hindostan,
of giving girls in marriage at a very early age, and in-
ducing sexual excitement previous to the proper menstrual
time. The menstrual functions continue through the

/

MENSTRUATION. 727

whole fruitful period of a woman’s life, and usually cease
between the forty-fifth and fiftieth years.

The several menstrual periods usually occur at intervals
of a lunar month, the duration of each being from three
to six days. In some women the intervals are as short as
three weeks or even less; while in others they are longer
than a month. The periodical return is usually attended
by pain in the loins, a sense of fatigue in the lower limbs,
and other symptoms, which are different in different indi-
viduals. Menstruation does not usually occur in pregnant .
women, or in those who are suckling; but instances of
its occurrence in both these conditions are by no means
rare.

The menstrual discharge consists of blood effused from
the inner surface of the uterus, and mixed with mucus
from the uterus, vagina, and external parts of the gene-
rative apparatus. Being diluted by this admixture, the
menstrual blood coagulates less perfectly than ordinary
blood; and the frequent acidity of the vaginal mucus
tends still further to diminish its coagulability. This has
led to the erroneous supposition that the menstrual blood
contains an unusually small quantity of fibrin, or none at
all. The blood-corpuscles exist in it in their natural state :
mixed with them may also be found numerous scales of
epithelium derived from the mucous passages along which
the discharge flows.

Corpus Luteum.

Immediately before, as well as subsequently to, the rup-
ture of a Graafian vesicle, and the escape of its ovum,
certain changes ensue in the interior of the vesicle, which
result in the production of a yellowish mass, termed a
corpus luteum.

When fully formed the corpus luteum of mammiferous

728 GENERATION AND DEVELOPMENT.

animals is a roundish solid body, ef a yellowish or orange
colour, and composed of a number of lobules, which sur-
round, sometimes a small cavity, but more frequently a
small stelliform mass of white substance, from which deli-
cate processes pass as septa between the several lobules.
Very often, in the cow and sheep, there is no white sub-
stance in the centre of the corpus luteum ; and the lobules
projecting from the opposite walls of the Graafian vesicle
appear in a section to be separated by the thinnest possible
lamina of semi-transparent tissue.

When a Graafian vesicle is about to burst and expel the
ovum, it becomes highly vascular and opaque; and, im-
mediately before the rupture takes place, its walls appear
thickened on the interior by a reddish glutinous or
fleshy-looking substance. Immediately after the rupture,
the inner layer of the wall of the vesicle appears pulpy and
flocculent. It is thrown into wrinkles by the contraction
of the outer layer, and, soon, red fleshy mammillary pro-
cesses grow from it, and gradually enlarge till they nearly »
fill the vesicle, and even protrude from the orifice in the
external covering of the ovary. Subsequently this orifice
closes, but the fleshy growth within still increases during
the earlier period of pregnancy, the colour of the substance
gradually changing from red to yellow, and its consistence
becoming firmer.

The corpus luteum of the human female (fig. 211) differs
from that of the domestic quadruped in being of a firmer
texture, and having more frequently a persistent cavity
at its centre, and in the stelliform cicatrix, which remains
in the cases where the cavity is obliterated, being propor-
tionately of much larger bulk. The quantity of yellow
substance formed is also much less: and, although the
deposit increases after the vesicle has burst, yet it does not
usually form mammillary growths projecting into the cavity
of the vesicle, and never protrudes from the orifice, as is

CORPUS LUTEUM, ~ 720

the case in other Mammalia. It maintains the character
of a uniform, or nearly uniform, layer, which is thrown into
wrinkles, in consequence of the contraction of the external
tunie of the vesicle. After the orifice of the vesicle has
closed, the growth of the yellow substance continues
during the first half of pregnancy, till the cavity is reduced
to a comparatively small size, or is obliterated; in the latter
case, merely a white stelliform cicatrix remains in the centre
of the corpus luteum.

An effusion of blood generally takes place into the cavity
of the Graafian vesicle at the time of its rupture, especially
in the human subject ; but it has no share in forming the
yellow body; it gradually loses its colouring matter, and
acquires the character of a mass of fibrin. The serum of
the blood sometimes remains included within a cavity in
the centre of the coagulum, and then the deoclorized fibrin
forms a membraniform sac, lining the corpus luteum. At

* Fig. 211. Corpora lutea of different periods. 38. Corpus luteum of
about the sixth week after impregnation, showing its plicated form at
that period. 1. Substance of the ovary. 2. Substance of the corpus
luteum. 3. A greyish coagulum in its cavity. After Dr. Paterson.
A. Corpus luteum, two days after delivery. vp. In the twelfth week
after delivery. After Dr. Montgomery.

730 GENERATION AND DEVELOPMENT.

other times the serum is removed, and the fibrin consti-
tutes a solid stelliform mass. |

The yellow substance of which the corpus luteum con-
sists, both in the human subject and in the domestic
animals, is a growth from the inner surface of the Graafian
vesicle, the result of an increased development of the cells
forming the membrana granulosa, which naturally lines
the internal tunic of the vesicle.

The first changes of the internal coat of the Graafian
vesicle in the process of formation of a corpus luteum, seem
to occur in every case in which an ovum escapes; as well ©
in the human subject as in the domestic quadrupeds. If
the ovum is impregnated, the growth of the yellow sub-
stance goes on during nearly the whole period of gestation,
and forms the large corpus luteum commonly described as
a characteristic mark of impregnation. If the ovum is
not impregnated, the growth of yellow substance on the
internal surface of the vesicle proceeds, in the human ovary,
no further than the formation of a thin layer, which shortly
disappears; but in the domestic animals it continues for
some time after the ovum has perished, and forms a corpus
luteum of considerable size. The fact, that a structure, in
its essential characters similar to, though smaller than, a
corpus luteum observed during pregnancy, is formed in the
human subject, independent of impregnation or of sexual
union, coupled with the varieties in size of corpora lutea
formed during pregnancy, necessarily renders unsafe all
evidence of previous impregnation founded on the existence
of a corpus luteum in the ovary.

The following table by Dalton, expresses well the dif-
ferences between the corpus luteum of the pregnant and
unimpregnated condition respectively. .

_IMPREGNATION OF THE OVUM. 731

Corpus LuTevmM oF MEN- - Corpus LurEvUM oF PREG-

At the end of

three weeks
One month

Two nonths —

STRUATION.

NANCY.

Three-quarters of an inch in diameter; central clot
reddish ; convoluted wall pale.

Smaller ; convoluted
wall bright yellow;
clot still reddish.

Reduced to the condition

Larger ; convoluted wall
bright yellow; clot still
reddish.

Seven-eighths of an inch in

_ Siz months Absent.

Nine months | Absent.

of an insignificant} diameter ; convoluted wall

cicatrix. bright yellow ; clot per-
fectly decolorised.

Still as large as at end of
second month ; clot fibri-
nous; convoluted: wall
paler.

One-half an inch in diame-
ter; central clot converted
into a radiating cicatrix ;
the external wall tolerably
thick and convoluted, but
without any bright yellow
colour.

IMPREGNATION OF THE OVUM.
Male Sexual Functions.

The fluid of the male, by which the ovum is impregnated,
consists essentially of the semen secreted by the testicles ;
and to this are added, as necessary, perhaps, to its per-
fection, a material secreted by the vesiculee seminales, in
which, as in reservoirs, the semen lies before its discharge,
as well as the secretion of the prostate gland, and of
Cowper’s glands. Portions of these several fluids are,
probably, all discharged, together with the proper secretion
of the testicles. |

The secreting structure of the testicle is disposed in two
contiguous parts, (1) the body of the testicle enclosed within
a tough fibrous membrane, the tunica albuginea, on the
outer surface of which is the serous covering formed by

' the tunica vaginalis, and (2) the epididymis. The vas deferens,

732 GENERATION AND DEVELOPMENT. .

the main trunk of the secreting tube, when followed back
to its origin, is found to pass to the lower part of the
epididymis, and assumes there a much less diameter with
a very tortuous course: with its various convolutions it
forms first the mass named globus minor, then the body, and
then the globus major of the epididymis. At the last-named
part, the duct divides into ten or twelve small branches,
the convolutions of which form coniform masses, named
cont vasculosi ; and the vessels continued from these, the vasa
efferentia, after anastomosing, one with another, in what is
called the rete testis, lead finally through the tubuli recti or
vasa recta to the tubules which form the proper substance of
the testicle, wherein they are arranged in lobules, closely
packed, and all attached to the tough
fibrous tissue at the back of the testicle.

The seminal tubes, or tubult seminifert,
which compose the proper substance
of the testicle, are fine thread-like
tubules, formed of simple homogene-
ous membrane, measuring on an
average ~1,th to z},th of an inch
in diameter, and lined with epithe-
lium or gland-cells. Rarely branching,
they extend as simple tubes through
a great length, with the same uniform
structure, and probably terminate
either in free closed extremities or in
loops. Their walls are covered with fine capillary blood-
vessels, through which, reckoning their great extent in

Fig. 212.* .

* Fig. 212. Plan of a vertical section of the testicle, showing the
arrangement of the ducts. The true length and diameter of the ducts
have been disregarded. a, a, tubuli seminiferi coiled up in the separate
lobes; b, tubuli recti or vasa recta; ¢, rete testis ; d, vasa efferentia

ending inthe coni vasculosi ; Z, ¢, g, convoluted canal of the epididymis ;

h, vas deferens ; J, section of the back part of the tunica albuginea ; 4, 4,
fibrous processes running between the lobes ; s, mediastinum.

THE STRUCTURE OF THE TESTICLE. 733.

A ; Fig. 213.* B

‘a

&

* Fig. 313. A, spermatic fila-
ments from the human vas deferens
(from K6lliker). 1, magnified 350
diameters ; 2, magnified 800 dia-
meters ; a, from the side; , from
above. B, spermatic cells and
spermatozoa of the bull undergoing
development (gpm. Kolliker) *3°.
I, spermatic cell&ayith one or two
nuclei, one of the ear ; 2, 3, free:
nuclei, with spe d
forming ; 4, the filar@e
and the body widened} 5, filaments
nearly fully developed: , escape
of the spermatozoa from their cells
in the same animal. 1, spermatic
cell containing the spermatozoon.
coiled up within it ; 2, the cells elon-
gated by the partial uncoiling of the
spermatic filament; 3, a cell from
which the filament has in part be-
come free; 4, the same with the
body also partially freé ; 5, sperma-

tozoon from the epididymis with vestiges of the ceil adherent ; 6, sper-
matozoon from the vas deferens, showing the small enlargement, 0, on

the filament.

734. GENERATION AND DEVELOPMENT.

comparison with the size of the spermatic artery, the
blood must move very slowly.

The seminal fluid secreted by the testicle is one of those.

secretions in which a process of development is continued
after its formation by the secreting cells, and its discharge
from them into the tubes. The ‘principal part of this
development consists in the formation of the peculiar
bodies named seminal filaments, spermatozoa or spermatozoids
(fig. 213), the complete development of which, in their full
proportion of number, is not achieved till the semen has
reached, or has for some time lain in, the vesiculee semi-
nales. LEarlier, after its first secretion, the semen contains
none of these bodies, but granules and round corpuscles
(seminal corpuscles), like large nuclei, enclosed within
parent-cells (fig: 213). Within reach of these corpuscles,
or nuclei, a seminal filament is developed, by a similar
process in nearly all animals. Each corpuscle, or nucleus,
is filled with granular matter; this is gradually converted
into a spermatozoid, which is at first coiled up, and in
contact with the inner surface of the wall of the corpuscle
(fig. 213, C, 1).

Thus developed, the human seminal filaments consist of
a long, slender, tapering portion, called the body or tail,
to distinguish it from the head, an oval or pyriform por-
tion of larger diameter, flattened, and sometimes pointed.
They are from ,3.,th to ;1,th of an inch in length, the
length of the head alone being from =,),,th to +54>th of

an inch, and its width about half as much. They present.

no trace of structure, or dissimilar organs; a dark spot
often observed in the head, is probably due to its. being
concave, like a blood corpuscle. They move about in the
fluid like so many minute corpuscles, with each a ciliary

process, lashing their tails, and propelling their heads .

forwards in various lines. Their movement, which is pro-
bably essentially, as well as apparently, similar to that of
ciliary processes, appears nearly independent of external

“ has ‘dl i eae 4

n THE SEMINAL FLUID. 735

conditions, provided the natural density of the fluid is pre-
served; disturbing this condition, by either evaporating
the semen or diluting it, will stop the movement. It
may continue within the body of the female for seven or
‘eight days, and out of the body for at least nearly twenty-
four hours. The direction of the movement is quite un-
certain: but in general, the current that each excites
keeps it from the contact of others. The rate of motion,
according to Valentin, is about one inch in thirteen
minutes. 3

Respecting the purpose served by these seminal fila-

ments, or concerning their exact nature, little that is
certain can be said. Their occurrence in the impregnating
fluid of nearly all classes of animals, proves that they are
essential to the process of impregnation; but beyond this,
and that their contact with the ovum is necessary for its
development, nothing is known.
_ The seminal fluid is, probably, after the period of puberty,
secreted constantly, though, except under excitement, very
slowly, in the tubules of the testicles. From these it passes
along the vasa deferentia into the vesicule seminales,
whence, if not expelled in emission, it may be discharged,
as slowly as it enters them, either with the urine, which
may remove minute quantities, mingled with the mucus of
the bladder and the secretion of the prostate, or from the
urethra in the act of defecation.

The vesicule seminales have the appearance of out-growths
from the vasa deferentia. Each vas deferens, just before
it enters the prostate gland, through part of which it
passes to terminate in the urethra, gives off a side-branch,
which bends back from it at an acute angle; and this
branch dilating, variously branching, and pursuing in both
itself and its branches a tortuous course, constructs the
vesicula seminalis. Each of the vesicule, therefore, might
be unravelled into a single branching tube, sacculated,
convoluted, and folded up.

736 GENERATION AND DEVELOPMENT.

The mucous membrane lining the vesicule seminales,
like that of the gall-bladder, is minutely wrinkled and set
with folds and ridges arranged so as to give it a finely
reticulated appearance. The rest of their walls is formed,
chiefly of a layer of organic muscular fibres, from which’

-

Fig. 214.* " _

they derive contractile power for the expulsion of their
contents.

To the vesicule seminales a double function may be
assigned; for they both secrete some fluid to be added to

* Fig.214. Dissection of the base of the bladder and prostate gland,
showing the vesicule seminales and vasa deferentia (from Haller).—a,
lower surface of the bladder at the place of reflexion of the peritoneum ;
b, the part above covered by the peritoneum ; 7, left vas deferens, ending
in ¢, the ejaculatory duct ; the vas deferens has been divided near 7, and
all except the vesicle portion has been taken away ;.s, left vesicula .
seminalis joining the same duct ; s, s, the right vas deferens and right
vesicula seminalis, which has been unravelled; py, under side of the =
prostate gland ; m, part of the uretha; uw, uw, the ureters (cut short
near /v), the right one turned aside.

THE VESICULH SEMINALES. 737

that of the testicles, and serve as reservoirs for the seminal
fluid. The former is their most constant and probably
most important office; for in the horse, bear, guinea-pig,
and several other animals, in whom the vesicule seminales
are large and of apparently active function, they do not
communicate with the vasa deferentia, but pour their
secretions, separately, though it may be simultaneously,
into the urethra. In man, also, when one testicle is lost,
the corresponding vesicula seminalis suffers no atrophy,
though its function as a reservoir is abrogated. But how
the vesiculz: seminales act as secreting organs is unknown ;
the peculiar brownish fluid which they contain after death
does not properly represent their secretion, for it is different
in appearance from anything discharged during life, and
is mixed with semen. It is nearly certain, however, that
their secretion contributes to the proper composition of the
impregnating fluid; for in all the animals in whom they
exist, and in whom the generative functions are exercised
at only one season of the year, the vesicule seminales,
whether they communicate with the vasa deferentia or not,
enlarge commeusurately with the testicles at the —
of that season.

That the vesicule are also reservoirs in which the semi-
nal fluid may lie for a time previous to its discharge, is
shown by their commonly containing the seminal filaments
in larger abundance than any portion of the seminal ducts
themselves do. The fluid-like mucus, also, which is often
discharged from the vesicule in straining during defeca-
tion, commonly contains seminal filaments. But no reason
can be given why this office of the vesicule should not be
equally necessary to all the animals whose testicles are
organized like those of man, or why in many animals the
vesiculze are wholly absent.

There is an equally complete want of information re-
specting the secretions of the prostate and Cowper's
- glands, their nature and purposes. That they contribute to
3 B

738 GENERATION AND DEVELOPMENT.

the right composition of the impregnating fluid, is shown
both by the position of the glands and by their enlarging
with the testicles at the approach of an animal’s breeding
time. But that they contribute only a subordinate part is
shown by the fact, that, when the testicles are lost, though
these other organs be perfect, all procreative power ceases.

The mingled secretions of all the organs just described,
form the semen or seminal fluid. Its corpuscles have been
already described (p. 734): its fluid part has not been
satisfactorily analysed: but Henle says it contains fibrin,
because shortly after being discharged, flocculi form in it
by spontaneous coagulation, and leave the rest. of it
thinner and more liquid, so that the filaments move in it
more actively.

Nothing has shown what it is that makes this fluid with
its corpuscles capable of impregnating the ovum, or (what
is yet more remarkable) of giving to the developing off-
spring all the characters, in features, size, mental disposi-
tion, and liability to disease, which belong to the father.
This is a fact wholly inexplicable: and is, perhaps, only
exceeded in strangeness by those facts which show that
the seminal fluid may exert such an influence, not only on
the ovum which it impregnates, but, through the medium
of the mother, on many which are subsequently impreg-
nated by the seminal fluid of another male. It has been
often observed, for example, that a well-bred bitch, if she
have been once impregnated by a mongrel dog, will not
bear thorough-bred puppies in the next two or three
litters after that succeeding the copulation with the
mongrel. But the best instance of the kind was in the
case of a mare belonging to Lord Morton, who, while he
was in India, wished to obtain a cross-breed between the
horse and quagga, and caused this mare to be covered by
a male quagga. The foal that she next bore had distinct
marks of the quagga, in the shape of its head, black bars
on the legs and shoulders, and other characters. After

INFLUENCE OF FETUS ON MOTHER. 739

this time she was thrice covered by horses, and every time
the foal she bore had still distinct, though decreasing,
marks of the quagga; the peculiar characters of the
quagga being thus impressed not only on the ovum then
impregnated, but on the three following ova impregnated
by horses. It would appear, therefore, that the constitu-
tion of an impregnated female may become so altered and
tainted with the peculiarities of the impregnating male,
through the medium of the foetus, that she necessarily
imparts such peculiarities to any offspring she may sub-
sequently bear by other males. Of the direct means by
which a peculiarity of structure on the part of a male is
thus transmitted, nothing whatever is known.

DEVELOPMENT.
Changes in the Ovum previous to the Formation of the Embryo.

Of the changes which the ovum undergoes previous to
the formation of the embryo, some occur while it is still in
the ovary, and are apparently independent of impreg-
nation: others take place after it has reached the Fallo-
pian tube. The knowledge we possess of these changes
is derived almost exclusively from observations on the
ova of mammiferous animals, especially the bitch and
rabbit: but it may be inferred that analogous changes
ensue in the human ovum.

Bischoff describes the yelk of an ovarian ovum after
coitus as being unchanged in its characters, with the single
exception of being fuller and more dense; it is still
granular, as before, and does not possess any of the cells
subsequently found in it. The germinal vesicle always
disappears, sometimes before the ovum leaves the ovary,
at other times not until it has entered the Fallopian tube ;
but always before the commencement of the metamorphosis
of the yell.

As the ovum approaches the middle of the Fallopian

tube, it begins to receive a new investment, consisting of
3 B2

740 GENERATION AND DEVELOPMENT,

a layer of transparent albuminous or glutinous substance,
which forms upon the exterior of the zona pellucida. It is
at first exceedingly fine, and owing to this, and to its
Fig. 215.* transparency, is not easily recog-

eee nized: but at the lower part of the
Fallopian tube it acquires consider-
able thickness.

About this time, that is to say,
during its passage through the Fal-
lopian tube, a very remarkable
change takes place in the interior
of the ovum. The whole yelk be-
comes constricted in the middle,
and surrounded by a furrow, which,
eradually deepening, at length’ cuts
the yelk in half, while the same
process begins almost immediately
in each half of the yelk, and cuts
it also in two. The same process
is repeated in each of the quarters,
and so on, until at last by continual
cleavings the whole yelk is changed
into a mulberry-like mass of small
and more or less rounded bodies,
sometimes called ‘‘vitelline spheres,”
the whole still enclosed by the zona
pellucida or vitelline membrane (fig.
215). Each of these little spherules contains a transparent
vesicle, like an oil-globule, which is seen with difficulty,
on account of its being enveloped by the yelk-granules
which adhere closely to its surface.

The cause of this singular subdivision of the yelk is

* Fig, 215. Diagrams of the various stages of cleavage of the yelk
(after Dalton),

CLEAVAGE OF THE YELK. 7A

quite obscure: though the immediate agent in its produc-
tion seems to be the central vesicle contained in each -
division of the yelk. Originally there was probably but
one vesicle, situated in the centre of the entire granular
mass of the yelk, and probably derived from the germinal
vesicle. This, by some process of multiplication, divides
and subdivides: then each division and subdivision attracts
around itself, as a centre, a certain portion of the sub-

stance of the yelk. |

About the time at which the mammiferous ovum reaches
the uterus, the process of division and subdivision of the
yelk appears to have ceased, its substance having been
resolved into its ultimate and smallest divisions, while its
surface presents a uniform finely-granular aspect, instead
of its late mulberry-like appearance. The ovum, indeed,
appears at first sight to have lost all trace of the cleaving
process, and, with the exception of being paler and more
translucent, almost exactly resembles the ovarian ovum,
its yelk consisting apparently of a confused mass of finely
granular substance. But on a more careful examination,
it is found that these granules are aggregated into
numerous minute spherical masses, each of which contains
a clear vesicle in its centre, but is not, at this period,
provided with an enveloping membrane, and possesses
none of the other characters of a cell. The zona pellucida,
and the layer of albuminous matter surrounding it, have
at this time the same character as when at the lower part
of the Fallopian tube.

The time occupied in the passage of the ovum, from the
ovary to the uterus, occupies probably eight or ten days in
the human female.

Shortly after this, important changes ensue. Lach of
the several globular segments of the yelk becomes sur-
rounded by a membrane, and is thus converted into a cell,
the nucleus of which is formed by the central vesicle, the
contents by the granular matter originally composing the

742 GENERATION AND DEVELOPMENT.

globule: these granules usually arrange themselves con-
centrically around the nucleus. When the peripheral cells,
which are formed first, are fully developed, they arrange
themselves at the surface of the yelk into a kind of mem-
brane, and at the same time assume a pentagonal or
hexagonal shape from mutual pressure, so as to resemble
pavement-epithelium. As the globular masses of the
interior are gradually converted into cells, they also pass
to the surface and accumulate there, thus increasing the
thickness of the membrane already formed by the more
superficial layer of cells, while the central part of the yell
remains filled only with a clear fluid. By this means the
yelk is shortly converted into a kind of secondary vesicle,
the walls of which are composed externally of the original
vitelline membrane, and within by the newly-formed
cellular layer, the blastodermic or germinal membrane, as it
is called. Very soon, however, the latter, by the develop-
ment of new cells, increases in thickness, and splits into
two layers, so that now the ovum has three coats. The
vitelline membrane on the outside, and, within this, the
outer and the inner layers of the blastodermic membrane.

Of the last-named layers, the superior or outer, which
lies next to the zona pellucida or vitelline membrane, is
called the serous layer; from it are developed the organs
of the animal system of the body, ¢.g., the bones, muscles,
and integuments. The inferior or inner layer, in contact
with the yelk itself, is named the mucous layer, and serves
for the formation of the internal or visceral system of
organs.

Changes of the Ovum within the Uterus.

Very soon after its formation, and division into two
layers, the blastodermic vesicle or membrane presents at
one point on its surface an opaque roundish spot, which is
produced by an accumulation of cells and nuclei of cells,
of less transparency than elsewhere. This space, the

THE LAMINZ DORSALES. 743

“area germinativa” or germinal area, is the part at which
the embryo first appears.

At first the area germinativa has a rounded form, but
it soon loses this and becomes Fig. 216. *
oval, then pear-shaped, and
while this change in form is
taking place, there gradually
appears in its centre a clear
space or area pellucida (fig.
216), bounded externally by
a@ more opaque circle, the
obscurity being due to the
greater accumulation of nu-
Cleated cells and nuclei at
that part than in the area sistihaiee

The first trace of the embryo in the centre of the area
pellucida consists of a shallow groove or channel, the

primitive groove (fig. 216), formed of the external or
serous fold of the germinal membrane, the groove being
wider at its anterior or cephalic extremity, and tapering
towards the opposite extremity.

Coincidently with the formation of the primitive groove,
two oval masses of cells, the lamine dorsales, appear, one
on each side of the groove. At first scarcely elevated above
the plane of the germinal membrane, they soon rise into
two prominent masses, the upper borders of which gradually
tend towards each other, turning inwards over the primi-
tive groove. The parts from opposite sides then unite,
and convert the primitive groove into a tube, large and
rounded in front, narrow and lancet-shaped behind, which
is the central canal of the cerebro-spinal axis, and contains
the rudimental spinal cord and brain, which are developed
in its interior (fig. 217).

* Fig. 216. (After Dalton.) Impregnated egg, with commencement
of formation of embryo; showing the area germinativa or embryonic
spot, the area pellucida, and the primitive groove or trace.

744 GENERATION AND DEVELOPMENT.

Immediately beneath, and in a line parallel with the
primitive groove, may be seen, about the same time, a
narrow linear mass of cells, the chorda dorsalis, which
forms the basis around which the bodies of the vertebree
are developed. The development of this column is early

indicated by the appearance of a few square, at first in-
distinct, plates, the rudiments of vertebre (fig. 217, p),
which begin to appear at about the middle of each dorsal
lamina.

* Fig. 217. Portion of the germinal membrane, with rudiments of
the embryo ; from the ovumof a bitch. The primitive groove, A, is not
yet closed, and at its upper or cephalic end presents three dilatations
B, which correspond to the three divisions or vesicles of the brain. At
its lower extremity the groove presents a lancet-shaped dilatation (sinus -
rhomboidalis) c. The margins of the groove consist of clear pellucid
nerve-substance. Along the bottom of the groove is observed a faint
streak, which is probably the chorda dorsalis. . Vertebral plates
(after Bischoff). .

THE UMBILICAL VESICLE. 745

While the dorsal laminz are closing over the primitive
groove, thickened prolonga-
tions of the same serous layer
are given off from the lower
margin of each of them, and
are named lamine viscerales
seu ventrales. These visceral
laminze by degrees bend
downwards and inwards, and
at length, enclosing a part of
the yelk, unite and form the
anterior walls of the trunk—
enclosing the abdominal cavity below, as the dorsal plates
enclose the cerebro-spinal canal above.

Fig. 218.*

Umbilical Vesicle.

The ventral laminz, as they extend downwards and in-
wards, at first proceed on the same plane with the inner
layer of the germinal membrane, which immediately lines
them. Soon, however, they show a tendency to turn in-
wards, so as to constrict the yelk, and enclose only a part
of it; and soon afterwards the yelk and the inner layer of
the germinal membrane that contains it, are separated into
two portions, one of which is retained within the body of
the embryo, while the other remains outside, and receives
the name of the umbilical vesicle (v, fig. 219). The cavity of
the latter communicates for some time with that of the
abdomen, through what is called the umbilicus, by means
of a gradually narrowing canal, called the vitelline duct; the
interior of the abdomen and that of the umbilical vesicle
being lined by a continuous layer of the inner stratum, or
mucous layer of the germinal membrane; while around
both of them is a continuation of the outer, or serous layer

* Fig, 218. Diagram showing vascular area in the chick. a. A a
pellucida, 6. Area vasculosa, c¢. Area vitellina. .

746 GENERATION AND DEVELOPMENT.

(fig. 219). From that portion of the mucous layer which
is now enclosed within the body of the — the intes-
tinal canal is developed.

Thus, by the constriction which the fold of germinal
membrane, in which the abdominal walls are formed, pro-
duces at the umbilicus, the body of the embryo becomes

* Fig. 219. Diagrammatic section showing the relation in a mammal
and in man between the primitive alimentary canal and the membranes
of the ovum. The stage represented in this diagram corresponds to
that of the fifteenth or seyenteenth day in the human embryo, previous
to the expansion of the allantois: ¢, the villous chorion ; a, the amnion ;
a’, the place of convergence of the amnion and reflection of the false
amnion a”, a", or outer or corneous layer ; ¢, the head and trunk of the
embryo, comprising the primitive vertebree and cerebro-spinal axis ; 7, ¢;
the simple alimentary canal in its upper and lower portions ; v, the yelk-
sac or umbilical vesicle; v 7, the vitello-intestinal opening; w, the —
allantois connected by a pedicle with the anal portion of the alimentary
canal,

THE AMNION AND ALLANTOIS. 747

in. great measure detached from the yelk-sac or umbilical
vesicle, though the cavity of the rudimentary intestine
still communicates with it through the vitelline or omphalo-
mesenteric duct, and contains part of the yelk substance
with which the vesicle was filled. The yelk-sac contains,
however, the greater part of the substance of the yelk,
and furnishes a source whence nutriment is derived for
the embryo. In birds, the contents of the yelk-sac afford
nourishment until the end of incubation: but in Mam-
malia, the office of the corresponding umbilical vesicle
ceases at a very early period, the quantity of yelk is small,
and the embryo soon becomes independent of it by the
connections it forms with the parent. Moreover, in birds,
as the sac is emptied, it is gradually drawn into the abdo-
men through the umbilical opening, which then closes over
it: but in Mammalia it always remains on the outside;
and as itis emptied it contracts (fig. 220), Fig. 220.*
shrivels up, and together with the part of
its duct external to the abdomen, is de-
tached and disappears either before, or
at the termiuation of intra-uterine life,
the period of its disappearance varying in
different orders of Mammalia.

When blood-vessels begin to be de-
veloped, they ramify largely over the
walls of the umbilical vesicle, and are atibeds concerned
in absorbing its contents and conveying them away for the
nutrition of the embryo.

The Amnion and Allantois.

At an early stage of development of the foetus, and some
time before the completion of the changes which have been
just described, two important structures, called respectively

* Fig. 220. Human embryo with umbilical vesicle ; about the fifth
week (after Dalton).

748 GENERATION AND DEVELOPMENT.

the amnion and the gilantois, begin to be formed—the am-
nion being developed by the external, and the allantois by
the internal layer of the blastodermic membrane.
Fig. 221.* The amnion is produced in the fol-
by lowing manner :—The external layer
C . of the blastodermic membrane is raised
GR \ up in the form of a fold around the
“|) ‘body of the embryo, so that the latter
ry appears as if sunk in a kind of de-
pression, with the outer layer of the
membrane raised up wall-like around
it. On section, the Nee is that represented in
fig. 221.

Soon the edges of es fold rising higher and higher
above and around the embryo, coalesce over it; and the
double layer of membrane at their place of junction being
absorbed, the two layers of which the fold was originally
made up are separated from each other (figs. 223,224). The
imner of the two forms the amnion, and remains continuous
with the integument of the feetus at the umbilicus; while
the outer layer, receding farther and farther, is fused and
forms one with the inner surface of the original vitelline
membrane, which in the meantime has undergone various
alterations to be immediately described (p. 751).

As the term of pregnancy advances, the amnion becomes
more and more separated from the body of the foetus by a
considerable quantity of fluid, the so-called liquor amnit.

During the process of development of the amnion, the
allantois (c, fig. 222) begins to be formed. Growing out
from or near the hinder portion of the intestinal canal, with
which it communicates, it is at first’a pear-shaped mass of
cells ; but becoming vesicular and very soon simply membra-
nous and vascular, it insinuates itself between the amniotic
folds, just described, and comes into close contact and

* Fig. 221. Diagram of fecundated egg (after Dalton). a, um-
bilical vesicle ; 0, ammiotic cavity ; ¢, allantois.

THE URACHUS. + 949

union with the outer of the two folds, which has itself, as
before said, become one with the external investing mem-
brane of the egg. As it grows, the Fig. 222*.
allantois becomes exceedingly vascu-
lar, and in birds (fig. 222), envelopes
the whole embryo—taking up vessels,
so to speak, tothe outer investing
membrane of the egg, and lining the
inner surface of the shell with a vas-
cularmembrane; by these means afford-
ing an extensive surface in which the
blood may be aérated. In the human subject and in
other mammalia, the vessels carried out by the allantois
are distributed only to a special part of the outer membrane,
at which a structure called the placenta is developed.

In Mammalia, as the visceral laminz close in the abdo-
minal cavity, the allantois is thereby divided at the umbi-
licus into two portions; the outer part, extending from the
- umbilicus to the chorion (p. 751), soon shrivelling; while
the inner part, remaining in the abdomen, is in part con-
verted into the urinary bladder; the portion of the inner
part not so converted, extending from the bladder to the
umbilicus, under the name of the urachus. After birth the
umbilical cord, and with it the external and shrivelled por-
tion of the allantois, are cast off at the umbilicus, while the
urachus remains as an impervious cord stretched from the
top of the urinary bladder to the umbilicus, in the middle
line of the body, immediately beneath the parietal layer of
the peritoneum. It is sometimes enumerated among the
ligaments of the bladder.

* Fig. 222. Fecundated egg with allantois nearly complete. a,
inner layer of amniotic fold ; }, outer layer, of ditto ; ¢, point where
the amniotic folds come in contact. The allantois is seen penetrating
between the outer and inner layers of the amniotic folds. This figure,
which represents only the amniotic folds and the parts within them,
should be compared with figs. 223, 224, in which will be found the
structures external to these folds,

750 GENERATION AND DEVELOPMENT.

It must not be supposed that the phenomena which have
been successively described, occur in any regular order one
after another. On the contrary, the development of one
part is going on side by side with that of another.

Fig. 223. Fig. 224.*

Development of Blood-vessels.

At an early period of development, and during the changes
just described, an accumulation of cells ensues between the
mucous and serous lamin at a part of the germinal mem-
brane named the area vasculosa (b, fig. 218). Within this
mass, which constitutes a third or middle layer of the blasto-
dermic membrane, is laid the foundation for the develop-
ment of the vascular system. At the circumference of the
vascular area, insulated red spots and lines make their
appearance, and these soon unite, so as to form a network
of vessels filled with blood. The margin of the vascular
layer is at first limited and quite circular, being bounded
by vessels united in a circulus venosus, or sinus terminalis,

* Figs. 223 and 224 (after Todd and Bowman). a, chorion with
villi. The villi are shown to be best developed in the part of the
chorion to which the allantois is extending; this portion ultimately
becomes the placenta. 8, space between the two layers of the amnion.
c, amniotic cavity. d, situation of the intestine, showing its connexion
with the umbilical vesicle. ¢, umbilical vesicle. jf, situation of heart
and vessels. 4g, allantois.

THE CHORION. 751

but it soon extends over the whole surface of the germinal
membrane. |

At about the same time, the rudimentary heart is formed
in the same layer of the germinal membrane. As shown
by Schwann, the blood-vessels are developed originally
from nucleated cells. These cells send out processes; the
processes from different cells unite; and in this way rami-
fications and a network are produced—vessels extending
from this network in the area vasculosa into the area
pellucida, and joining the rudimentary heart (see p. 765).

The Chorion.

It has been already remarked that the allantois is a
structure which extends from the body of the footus to the
outer investing membrane of the ovum, that it insinuates
itself between the two layers of the amniotic fold, and
becomes fused with the outer layer, which has itself
become previously fused with the vitelline membrane.
By these means the external investing membrane of the
ovum, or the chorion, as it is Pig. 225,
now called, represents three
layers, namely, the original vi-
telline membrane, the outer
layer of the amniotic fold, and
the allantois.

Very soon after the entrance of
the ovum into the uterus, in the
human subject, the outer surface
of the chorion is found beset with
fine processes, the so-called villi of
thechorion(a, figs.22 3, 224), which
give ita rough and shaggy ap-
pearance. At first only cellular in structure, these little
outgrowths subsequently become vascular by the develop-
ment in them of loops of capillaries (fig. 225); and the latter
at length from the minute extremities of the blood-vessels
which are, so to speak, conducted from the foetus to the

752 GENERATION AND DEVELOPMENT.

chorion by the allantois. The function of the villi of
the chorion is evidently the absorption of nutrient matter
for the foetus; and this is probably supplied to them
at first from the fluid matter secreted by the follicular
glands of the uterus, in which they are soaked. Soon,
however, the footal vessels of the villi come into more
intimate relation with the vessels of the uterus. The part
at which this relation between the vessels of the foetus and

those of the parent ensues, is not, however, over the whole

surface of the chorion: for, although all the villi become
vascular, yet they become indistinct or disappear except at
one part where they are greatly developed, and by their
branching give rise, with the vessels of the uterus, to the
formation of the placenta.

To understand the manner in which the fetal and:

maternal blood-vessels come into relation with each other
in the placenta, it is necessary briefly to notice the changes
which the uterus undergoes after impregnation. These
changes consist especially of alterations in structure of the
superficial part of the mucous membrane which lines the
interior of the uterus, and which forms, after a kind of
development to be immediately described, the membrana
decidua, so called on account of its being discharged from
the uterus at the period of parturition.

Changes of the Mucous Membrane of the Uterus, and Formation
of the Placenta.

The mucous membrane of the human uterus is abun-
dantly beset with tubular follicles, arranged perpen-
dicularly to the surface. These follicles are very small in
the unimpregnated uterus; but when examined shortly
after impregnation, they are found elongated, enlarged,
and much waved and contorted towards their deep and
closed extremity, which is implanted at some depth in the
tissue of the uterus, and commonly dilates into two or
three closed sacculi (fig. 226).

—_—— -- -

THE GLANDS OF THE UTERUS. . 753

According to Dr. Sharpey, the glands of the mucous
membrane of the bitch’s uterus (and according to H.
Miiller, that of the human female also) are of two kinds,

Fig. 226.*

Son SN

Se

LM AME ic

simple and compound. The former, which are the more
numerous, are merely very short unbranched tubes closed
at one end (fig. 227, 1, 1), the latter (*,”) have a long duct
dividing into convoluted branches; both open on the inner
surface of the membrane by small round orifices, lined
with epithelium and set closely together.
~ On the internal surface Fig. 227.t
of the mucous membrane
may be seen the circular
orifices of the | glands,
many of which are, in the
early period of pregnancy,
surrounded by a whitish IMS)
ring, formed of the epi- Gi DOSE “
eon which lines the ) InantaaCildin
follicles (fig. 228).
Coincidently with the increasing size of the follicles, the
quantity of their secretion is augmented, the vessels of

YW

* Fig. 226. Section of the lining membrane of a human uterus at the
period of commencing pregnancy, showing the arrangement and other
peculiarities of the glands, d, d, a, with their orifices, a, a, a, on the
internal surface of the organ. Twice the natural size.

+ Fig. 227. A vertical section of the mucous membrane showing
uterine glands of the bitch, magnified twelve diameters ; 1, 1, simple

glands ; 2, 2, compound ditto (from Sharpey). 63

704 - GENERATION AND DEVELOPMENT.

the mucous membrane become larger and more numerous,
while a substance composed chiefly of nucleated cells fills
up the interfollicular spaces in which the blood-vessels are

Fig. 228.* contained. The effect of
these changes is an in-
creased thickness, softness,
and vascularity of the mu-
cous membrane, the super-
ficial part of which itself
forms the membrana de-
cidua.

The object of this in-
creased development seems
to be the production. of
nutritive materials for the
ovum; for the cavity of the uterus shortly becomes filled
with secreted fluid, consisting almost entirely of nucleated
cells, in which the villi of the chorion are embedded.

When the ovum first enters the uterus it becomes im-
bedded in the structure of the decidua, which is yet quite
soft, and in which soon afterwards three portions are dis-
tinguishable. These have been named the decidua vera, the
decidua reflexa, and the decidua serotina. The first of these,
the decidua vera, lines the cavity of the uterus; the second,
or decidua reflewa, is a part of the decidua vera, which
grows up around the ovum, and, wrapping it closely, forms
its immediate investment. The third, or decidua serotina,
is the part of the decidua vera which becomes especially
developed in connection with those villi of the chorion
which, instead of disappearing, remain to form the footal
part of the placenta.

* Fig. 228. Two thin segments of human decidua after recent im-
pregnation, viewed on a dark ground : they show the openings on the
surface of the membrane. A is magnified six diameters, and B twelve
diameters. At 1, the lining of epithelium is seen within the orifices, at

2 it has escaped (from Sharpey).

THE PLACENTA. + 765

As the ovum increases in size, the decidua vera and the
decidua reflexa gradually come into contact, and in the
third month of pregnancy the cavity between them has quite
disappeared. Henceforth it is very difficult, or even impos-
sible, to distinguish the two layers.

During these changes the deeper part of the mucous
membrane of the uterus, at and near the region where the
placenta is placed, becomes hollowed out by sinuses, or
¢avernous spaces, which communicate on the one hand
with arteries and on the other with veins of the uterus.

~Into these sinuses the villi of the chorion protrude, pushing
the thin wall of the sinus before them, and so come into
intimate relation with the blood contained in them.
There is no direct communication between the blood-vessels
of the mother and those of the foetus; but the layer or
layers of membrane intervening between the blood of the
one and of the other offer no obstacle to a free inter-
change of matters between them. Thus the villi of the
chorion, containing foetal blood, are bathed or soaked in
maternal blood contained in the uterine sinuses. The
arrangement may be roughly compared to filling a glove
with foetal blood, and dipping its fingers into a vessel con-
taining maternal blood. But in the foetal villi there is a
constant stream of blood into and out of the loop of capil-
lary blood-vessel contained in it, as there is also into and
out of the maternal sinuses.

It would seem from the observations of Professor
Goodsir, that, at the villi of the placental tufts, where the
foctal and maternal portions of the placenta are brought
into close relation with each other, the blood in the vessels
of the mother is separated from that in the vessels of the
foetus by the intervention of two distinct sets of nucleated
cells (fig. 229). One of these (b) belongs to the maternal
portion of the placenta, is placed between the membrane of
the villus and that of the vascular system of the mother,

and is probably designed to separate from the blood of the
-« 3¢2

756 GENERATION AND DEVELOPMENT..

parent the -materials destined for the blood of the foetus ; _
the other (f) belongs to the foetal portion of the placenta,
is situated between the membrane of the villus and
the loop of vessels contained within, and probably serves
for the absorption of the material secreted by the other
sets of cells, and for its conveyance into the blood-vessels
of the footus.. Between the two sets of cells with
their investing membrane there exists a space (d),

Fig. 229.* into which it is probable that the

| materials secreted by the one set of
cells of the villus are poured in
order that they may be absorbed
by the other set, and thus conveyed
into the foetal vessels.

Not only, however, is there a pas-
sage of materials from the blood of
the mother int that of the foetus, but there can be no doubt
of the existence of a mutual interchange of materials between —
the blood both of foetus and of parent, the latter supplying
the former with nutriment, and in turn abstracting from it
materials which require to be removed. Dr. Alexander
Harvey’s experiments were very decisive on this point.
The view has also received abundant support of late from
Mr. Hutchinson’s important observations on the communi-
eation of syphilis from the father to the mother, through
the instrumentality of the foetus; and still more from
Mr. Savory’s experimental researches, which prove quite
clearly that the female parent may be directly inoculated
through the fotus. Having opened the abdomen and
uterus of a pregnant bitch, Mr. Savory injected a solution

* Fig. 229. Extremity of a placental villus. a, lining membrane
of the vascular system of the mother; 6, cells immediately lining a ;
d, space between the maternal and feetal portions of the villus; ¢,
internal membrane of the villus, or external membrane of the chorion ;
f, internal cells of the villus, @f cells of the chorion ; g, loop of umbilical
vessels (after Goodsir).

“

THE PLACENTA. 757

of strychnia into the abdominal cavity of one foetus, and

into the thoracic cavity of another, and then replaced all
the parts, every precaution being taken to prevent escape
of the poison. In less than half an hour, the bitch died
from tetanic spasms; the foetuses operated on were also
found dead, while the others were alive and active. The
experiments, repeated on other animals with like results,
leave no doubt of the rapid and direct transmission of
matter from the foetus to the mother, through the blood of
the placenta.

The placenta, therefore, of the human subject is com-
posed of a fetal part and a maternal part,—the term,
placenta, properly including all that entanglement of foetal
villi and maternal sinuses, by means of which the blood
of the foetus is enriched and purified after the fashion
necessary for the proper growth and development of those
parts which it is destined to nourish.

The whole of this structure is not, as might be imagined,
thrown off immediately after birth. The greater part,
indeed, comes away at that time, as the after-birth, and the
separation of this portion takes place by a rending or crush-
ing through of that part at which its cohesion is least strong,
namely, where it is most burrowed and undermined by the
cavernous spaces before referred to. In this way it is cast
off with the footal membranes and the decidua vera and
veflexa, together ‘sith, a part of the decidua serotina.
The remaining portion withers, and disappears by being
gradually either,absorbed, or thrown off in the uterine
discharges or the lochia, which occur at this period.

A new muceus meftabrane is of course gradually de-
veloped, as the old one, by its peculiar transformation into
what is called the decidua, ceases to perform its original
functions.

The umbilical cord, which in the latter part of foetal life
is almost solely composed of the two arteries and the single
vein which respectively convey foetal blood to and from the

758 GENERATION AND DEVELOPMENT.

placenta, contains the remnants of other structures which
in the early stages of the development of the embryo were,
as already related, of great comparative importance. Thus,
in early foetal life, it is composed of the following parts :
—(1). Externally, a layer of the amnion, reflected over it
from the umbilicus, (2). The umbilical vesicle with its
duct and appertaining omphalo-mesenteric blood-vessels.
(3). The remains of the allantois, and continuous with it
the urachus. (4). The umbilical vessels, which, as just
remarked, ultimately form the greater part of the cord.

DEVELOPMENT OF ORGANS,

It remains now to consider in succession the develop-
ment of the several organs and systems of organs in the
further progress of the embryo.

Development of the Vertebral Column and Cranium.

The primitive part of the vertebral column in ali the
Vertebrata is the gelatinous chorda dorsalis, which con-
sists entirely of cells. This cord tapers to a point at
the cranial and caudal extremities of the animal. In the
progress of its development, it is found to become enclosed
in a membranous sheath, which at length acquires a fibrous
structure, composed of transverse annular fibres. The
chorda dorsalis is to be regarded as the azygos axis of
the spinal column, and, in particular, of the future bodies
of the vertebre, although it never itself passes into the
cartilaginous or osseous state, but remains enclosed as in a
case within the persistent parts of the vertebral column
which are developed around it. It is permanent, however,
only in a few animals: in the majority it disappears at an
early period.

The cartilaginous or osseous vertebrae are always first
developed in pairs of lateral elements at the sidés of the

| Fan
Se,

DEVELOPMENT OF VERTEBRZ. 759

chorda dorsalis. From these lateral elements are formed
the bodies and the arches of the vertebre. In some
animals, as the sturgeon, however, the lateral elements of
the vertebree undergo no further development, and. it is
here that the chorda dorsalis is persistent through life.
In the myxinoid fishes the spinal column presents no ver-
tebral segments, and there exists merely the chorda
dorsalis with the fibrous layer surrounding its sheath,
which is the layer in which the skeleton originates.
This fibrous layer also forms superiorly the membranous
covering of the vertebral canal.

In reptiles, birds, and mammals, the mode in which the
vertebrze are formed around the chorda dorsalis seems to
be different. When the formation of these parts from
the blastema commences, there appears at each side of
the chorda dorsalis a series of quadrangular figures,
the rudiments of the future vertebrae. These gradually
increase in number and size, so as to surround the
chorda both above and below, sending out, at the same
time, superiorly, processes to form the arches destined to
enclose the spinal cord. In this primitive condition the
body and arches of each vertebra are formed by one piece
on each side. At a certain period these two primary
elements, which have become cartilaginous, unite in-
feriorly by a suture. The chorda is now enclosed in a
case, formed by the bodies of the vertebree, but it gradually
wastes and disappears. Before the disappearance of the
chorda, the ossification of the bodies and arches of the
vertebree begins at distinct points.

The ossification of the body of a vertebra is first ob-
served at the point where the two primitive elements of
the vertebree have united inferiorly. Those vertebre
which do not bear ribs, such as the cervical vertebre,
have generally an additional centre of ossification in the
transverse process, which is to be regarded as an abortive
rudiment of a rib. In the foetal bird, these additional

760 GENERATION AND DEVELOPMENT.

ossified portions exist in all the cervical vertebrae, and
gradually become so much developed in the lower part of
the cervical region as to form the upper false ribs of this
class of animals. The same parts exist in mammalia and
man; those of the last cervical vertebree are the most
developed, and in children may, for a considerable period,
be distinguished as a separate part on each side, like the
root or head of a rib. ;

The true cranium is a prolongation of the vertebral
column, and is developed at a much earlier period than the
facial bones. Originally, it is formed of but one mass, a
cerebral capsule, the chorda dorsalis being continued into
its base, and ending there with a tapering point. This
relation of the chorda dorsalis to the basis of the cranium
is persistent through life in some fish, e.g., the sturgeon.
The first appearance of a solid support at the base of
the cranium observed by Miiller in fish, consists of two
elongated bands of cartilage, one on the right and the
other on the left side, which are connected with the car-
tilaginous capsule of the auditory apparatus, and united
with each other in an arched manner, anteriorly beneath
the anterior end of the cerebral capsule. Hence, in the
cranium, as in the spinal column, there are at first de-
veloped at the sides of the chorda dorsalis two symmetrical
elements, which subsequently coalesce, and may wholly
enclose the chorda.*

Development of the-Hace and Visceral Arches.

It has been said before that at an early period of
development of the embryo, there grow up on the sides of
the primitive groove the so-called dorsal lamine, which at

* For much new and original matter relating to the development of
the cranium, the reader is referred to the important lectures on Com-
parative Anatomy, delivered at the College of Surgeons by Professor
Huxley,

THE VISCERAL ARCHES AND CLEFTS. 7OL

length coalesce, and complete by their union the spinal
canal, The same process essentially takes place in the
head, so as to enclose the cranial cavity. i

The so-called visceral lamine have been also described
as passing forwards, and gradually coalescing in front, as
the dorsal lamine do behind, and thus enclosing the
thoracic and abdominal cavity. An
analogous process occurs in the facial
and cervical regions, but the enclosing
laminz, instead of being simple, as in
the former instances, are cleft.

In this way the so-called visceral arches
and clefts are formed, four on each side
(fig. 230 a), and from or in connection
with these arches the following parts are
developed :—

From the first arch, and its maxillary
process, the superior mawillary, the palate
bone, and the internal pterygoid plate of
the sphenoid bone, the.incus and malleus
and the lower jaw. The upper part of the
face in the middle line is developed from
the so-called fronto-nasal process (A, 3,
fig. 230). From the second arch are de-
veloped the stapes, the stapedius muscle,
the styloid process of the temporal bone,

Mi,

i

Wl

* Fig. 2304. Magnified view from before of the head and neck of a
human embryo of about three weeks (from Ecker)—1, anterior cerebral
vesicle or cerebrum ; 2, middle ditto ; 3, middle or fronto-nasal process ;
4, superior maxillary process ; 5, eye ; 6, inferior maxillary process, or
first visceral arch, and below it the first cleft; 7, 8, 9, second, third,
and fourth arches and clefts. 3, anterior view of the head of a
human foetus of about the fifth week (from Ecker, as before, fig. 1V.).
I, 2, 3, 5, the same partsasin A ; 4, the external nasal or lateral frontal
process; 6, the superior maxillary process; 7, the lower jaw; +,
the tongue; 8, first branchial cleft becoming the meatus auditorius
externus,

762 GENERATION AND DEVELOPMENT.

the stylo-hyoid ligament, and the smaller cornu of the hyoid
bone. From the third visceral arch, the greater cornu and

body of the hyoid bone. In man and other mammalia the -

fourth visceral arch is indistinct.
Development of the Extremities.

The extremities are developed in an uniform manner in
all vertebrate animals. They appear in the form of leaf-
like elevations from the parietes of the trunk (see fig.
231), at points where more or less of an arch will be pro-
duced for them within. The primitive form of the ex-

Fig. 231.*

i
“tp

tremity is nearly the same in all Vertebrata, whether it be
destined for swimming, crawling, walking, or flying. In
the human footus the fingers are at first united, as if
webbed for swimming; but this is to be regarded not so

* Fig. 231. A human embryo of the fourth week, 33 lines in length.
1, the chorion ; 3, part of the amnion; 4, umbilical vesicle with its long
pedicle passing into the abdomen ; 7, the heart; 8, the liver ; 9, the
visceral arch destined to form the lower jaw, beneath which are two
other visceral arches separated by the branchial clefts ; 10, rudiment of
the upper extremity ; 11, that of the lowerextremity ; 12, the umbilical
cord; 15, the eye ; 16, the ear; 17, the cerebral hemispheres; 18, the
optic lobes or corpora quadrigemina. ‘

1

DEVELOPMENT OF VASCULAR SYSTEM. 76 3

much as an approximation to the form of aquatic animals
as the primitive form of the hand, the individual parts of
which subsequently become more completely isolated.

Development of the Vascular System.

The first development of the vascular system and heart in
the germinal membrane has been already alluded to (p. 750).
The earliest form of the heart presents itself as a solid
compact mass of embryonic cells, similar to those of which
the other organs of the body are constituted. It is at first
unprovided with a cavity; but this shortly makes its ap-
pearance, resulting apparently from the separation from
each other of the cells of the central portion. A liquid
is now formed in the still closed cavity, and the central
cells may be seen floating within it. These contents of the
cavity are soon observed to be propelled to and fro with a
tolerable degree of regularity, owing to the commencing
pulsations of the heart. These pulsations take place even
before the appearance of a cavity, and immediately after
the first ‘laying down’ of the cells from which the heart
is formed. At first they seldom exceed from fifteen to
eighteen in the minute. The fiuid within the cavity of
the heart shortly assumes the characters of blood. At the
same time the cavity itself forms a communication with
the great vessels in contact with it, and the cells of which
its wall are composed are transformed into fibrous and
muscular tissues, and into epithelium.

Blood-vessels appear to be developed in two ways,
according to the size of the vessels. In the formation of
large blood-vessels, masses of embryonic cells similar to
those from which the heart and other structures of the
embryo are developed, arrange themselves in the position,
form, and thickness of the developing vessel. Shortly after-
wards the cells in the interior of a column of this kind
seem to be developed into blood-corpuscles, while the

704 GENERATION AND DEVELOPMENT.

external layer of cells is converted into the walls of the
‘vessel. |

In the development of capillaries another plan is pur-.

Fig. 232.*

ory

* Fig. 232. Capillary blood-vessels of the tail of a young larval

frog. Magnified 350 times (after Kolliker).—a, capillaries permeable
to blood ; 6, fat-granules attached to the walls of the vessels, and con-
cealing the nuclei; ¢, hollow prolongation of a capillary, ending in a

point; d, a branching cell with nucleus and fat-granules ; it communi-

cates by three branches with prolongation of capillaries already formed ;
é, ¢, blood-corpuscles still containing granules of fat.

—

:
$
%

>

DEVELOPMENT OF VASCULAR SYSTEM. 705

sued. This has been well illustrated by Kolliker, as ob-
served in the tails of tadpoles. The first lateral vessels of
the tail have the form of simple arches, passing between
the main artery and vein, and are produced by the junc-
tion of prolongations, sent from both the artery and vein,
with certain elongated or star-shaped cells, in the sub-
stance of the tail. When these arches are formed and are
permeable to blood, new prolongations pass from them,
join other radiated cells, and thus form secondary arches.
In this manner, the capillary net-work extends in propor-
tion as the tail increases in length and breadth, and it, at
the same time, becomes more dense by the formation, ac-
cording to the same plan, of fresh vessels within its meshes.
The prolongations by which the vessels communicate with
the star-shaped cells consist at first of narrow-pointed
projections from the side of the vessels, which gradually
elongate until they come in contact with the radiated pro-
cesses of the cells. The thickness of such a prolongation
often does not exceed that of a fibril of fibrous tissue, and
at first it is perfectly solid; but, by degrees, especially
after its junct?on with a cell, or with another prolongation,
or with a vessel already permeable to blood, it enlarges,
and a cavity then forms in its interior (see fig. 232). With
Ko6lliker’s account, our own observations, made on the fine
gelatinous tissue conveying the umbilical vessels of a sheep’s
embryo to the uterine cotyledons, completely accord. This
tissue is well calculated to illustrate the various steps in the
development of blood-vessels from elongating and branch-
ing cells.

About the time that the heart at its lowest extremity
receives the venous trunks, and at its upper extremity
gives off the large arterial trunk, it becomes curved from a
straight into a horse-shoe form, and shortly divides into
three cavities (fig. 233). Of these three cavities, which are
developed in all Vertebrata, the most posterior is the sim-
ple auricle ; the middle one the simple ventricle; and the

766 GENERATION AND DEVELOPMENT.

most anterior the bulbus arteriosus. These three parts of
the heart contract in succession. The auricle and the
bulbus arteriosus at this period lie at the extremities of the
horse-shoe. The bulging out of the middle portion in-
feriorly gives the first indication of the future form of the
ventricle (see fig. 233). The great curvature of the horse-

Fig. 233.*

a fi
+ it &
X 1 : " ~
2 2S :

Pat =

shoe by the same means becomes much more developed
than the smaller curvature between the auricle and bulbus;
and the two extremities, the auricle and bulb, approach
each other superiorly, so as to produce a greater resem-
blance to the latter form of the heart, whilst the ventricle
becomes more and more developed inferiorly. The heart
of fishes retains these three cavities, no further division by
internal septa into right and left chambers taking place.
In Amphibia, also, the heart throughout life consists of the
three muscular divisions which are so early formed in the
embryo; but the auricle is divided internally by a septum
into a pulmonary and systemic auricle. In reptiles, not
merely the auricle is thus divided into two cavities, but a
similar septum is more or less developed in the ventricle.
In birds, mammals, and the human subject, both auricle
and ventricle undergo complete division by septa; whilst
in these animals, as well as in reptiles, the bulbus aorte is
not permanent, but becomes lost in the ventricles. The
septum dividing the ventricle commences at the apex and
extends upwards. When it is complete, a septum is
developed in the bulbus aortz, separating the roots of the

* Fig. 233. Heart of the chick at the 45th, 65th, and 85th hours of
incubation. 1, the venous trunks ; 2, the auricle ; 3, the ventricle ;
4, the bulbus arteriosus (after Dr. Allen Thomson).

THE FETAL CIRCULATION, 767

proper aorta and the pulmonary artery. The septum of
the auricles is developed from a semilunar fold, which
extends from above downwards. In man, the septum
between the ventricles, according to Meckel, begins to be
formed about the fourth week, and at the end of eight
weeks is complete. The septum of the auricles, in man
and all animals which possess it, remains imperfect
throughout foetal life. When the partition of the auricles
is first commencing, the two ven cavee have different re-
lations to the two cavities. The superior cava enters, as
‘in the adult, into the right auricle; but the inferior cava
is so placed that if appears to enter the left auricle, and
the posterior part of the septum of the auricles is formed
by the Eustachian valve, which extends from the point of
entrance of the inferior cava. Subsequently, however, the
septum, growing from above downwards, becomes directed
more and more to the left of the vena cava inferior.
During the entire period of foetal life, there remains an
opening in the septum, which the valve of the foramen
ovale, developed in the third month, imperfectly closes.

Circulation of Blood in the Fetus.

The circulation of blood in the foetus is peculiar, and
differs considerably from that of the adult. It will be
well, perhaps, to begin its description by tracing the
course of the blood, which, after being carried out to
the placenta by the two umbilical arteries, has returned,
cleansed and replenished, to the foetus by the umbilical
vein.

It is at first conveyed to the under surface of the liver,
and there the stream is divided,—a part of the blood
passing straight on to the inferior vena cava, through a
venous canal called the ductus venosus, while the remainder
passes into the portal vein, and reaches the inferior vena
cava only after circulating through the liver. Whether,
however, by the direct route through the ductus venosus

768 GENERATION AND DEVELOPMENT.

or by the roundabout way through the liver,—all the
blood which is returned from the placenta by the umbili-
cal vein reaches the inferior vena cava at last, and is

Fig. 234.

RiCom.Curotia d
L: Com.Carolid

'

'
.!
“

L. Sabclav.

—Laa\pect Art.

: ] IM <\ PetmY
a cig “s : { ; = “ rtery

é | f; fy a iS on L. Aurich
R. Auricle--| Ne

----Aortat
\V

- inferior Venu Cane,
’

-\--Aorta
0

\
Ww)

|
Ny
} |

4

Umbilicus - iG
fpr

V7 Wr ye Lliac *

Yer ~ L.Hy agaastrie,

> Arey SS
: ( } NS

| -+--2ixck. Lliae

carried by it to the right auricle of the heart, into which
cavity is also pouring the blood that has circulated in the
nead and neck and arms, and has been brought to the

THE FETAL CIRCULATION. 769

auricle by the superior vena cava. It-might be naturally
expected that the two streams of blood would be mingled
in the right auricle, but such is not the case, or only to a
slight extent. The blood from the superior vena cava,—
the less pure fluid of the two—passes almost exclusively
into the right ventricle, through the auriculo-ventricular
opening, just as if does in the adult; while the blood of
the inferior vena cava is directed by a fold of the lining
membrane of the heart, called the Eustachian valve, through
the foramen ovale into the left auricle, whence it passes
into the left ventricle, and out of this into the aorta, and
thence to all the body. The blood of the superior vena
cava, which, as before said, passes into the right ventricle,
is sent out thence in small amount through the pulmonary
artery to the lungs, and thence to the left auricle, as in
the adult. The greater part, however, by far, does not
go to the lungs, but instead, passes through a canal, the
ductus arteriosus, leading from the pulmonary artery into
the aorta just below the origin of the three great. vessels
which supply the upper parts of the body; and there
meeting that part of the blood of the inferior vena cava
which has not gone into these large vessels, it is dis- .
tributed with it to the trunk and lower parts,—a portion
passing out by way of the two umbilical arteries to the
placenta. From the placenta it is returned by the um-
bilical vein to the under surface of the liver, from which
the description started.

After birth the foramen ovale closes, and so do the
ductus arteriosus and ductus venosus, as well as the um-
bilical vessels; so that the two streams of blood which
arrive at the right auricle by the superior and inferior
vena cava respectively, thenceforth mingle in this cavity of
the heart, and passing into the right ventricle, go by way
of the pulmonary artery to the lungs, and through these,
after purification, to the left auricle and ventricle, to be

distributed over the body. (See chapter on Circulation.)
3D

770 GENERATION AND. DEVELOPMENT.

Development of the Nervous System.

The mode in which the rudimentary structures of the
cerebro-spinal nervous system are formed, has been already
stated (p. 743). The dorsal laminz, the inner borders of
which close in and form the canal of the spinal cord, seem
to leave a fissure in the situation of the medulla oblongata.
Between this and the most anter or extremity of the canal,
three vesicular enlargements, the vesicles of the brain, are.
developed (see fig. 217), and from these again are developed
the following parts :—

From the anterior primary vesicle—the optic thalami,
corpora striata, the third ventricle, and the cerebral
hemispheres, together with some other parts in connec-
tion with those above named, as the corpus callosum,
fornix, etc.

From the middle primary vesicle—the corpora quadrige-
mina and crura cerebri, with the aqueduct of Sylvius.

From the posterior primary, vesicle—the cerebellum, pons
Varolii, medulla oblongata, etc.

Development of the Organs of Sense.

The eye is in part developed as a protruded portion of
the first primary cerebral vesicle ; while passing backwards,
and pressing on the front of this process or primary optic

Fig. 235.*

* Fig. 235. Longitudinal section of the primary optic vesicle in the
chick magnified (from Remak).—A, from an embryo of sixty-five hours ;
B, afew hours later; C, of the fourth day; ¢, the corneous layer or
epidermis, presenting in A, the open depression for the lens, which is

sucess

_— ee a ee |

DEVELOPMENT OF THE EYEBALL. 77 I

vesicle, is a pouch of the common integument, which sub-
sequently becomes a shut sac, and in which is developed
the lens and its capsule (fig. 236). Subsequently there is

Fig. 236.*

protruded from below upwards, between the lens in front
and the primary optic vesicle behind, another process or

closed in B and C; 7, the lens follicle and lens ; pr, the primary optic
vesicle ; in A and B, the pedicle is shown ; in C, thesection being to the
side of the pedicle, the latter is not shown; v, the secondary ocular
vesicle and vitreous humour.

* Fig. 236. Diagrammatic sketch of a vertical longitudinal section
through the eyeball of a human feetus of four weeks (after Kolliker) *2°. —
—The section is a little to the side, so as to avoid passing through the
ocular cleft: c, the cuticle where it becomes later the cornea ; 7, the
lens ; 0, p, optic nerve formed by the pedicle of the primary optic vesicle ;
vp, primary medullary cavity or optic vesicle ; y, the pigment layer of
the choroid coat of the outer wall ; 7, the inner wall forming the retina ;
v s, secondary optic vesicle containing the rudiment of the vitreous
humour.

+ Fig. 237. Transverse vertical section of the eyeball of a human
embryo of four weeks (from Kolliker) *$°.—The anterior half of the
section is represented : y, 7, the remains of the cavity of the primary
optic vesicle ; p, the inner part of the outer layer forming the choroidal
pigment ; 7, the thickened inner part giving rise to the columnar and
other structures of the retina ; 7, the commencing vitreous humour
within the secondary optic vesicle ; v’, the ocular cleft through which
the loop of the central blood-vessel, a, projects from below ; J, the lens
with a central cavity.

3D 2

772 GENERATION AND DEVELOPMENT.

pouch, remaining for some time imperfect below, and
called the secondary optic vesicle. The deficiency below
contracts into what is called the ocular cleft, which subse-
quently becomes entirely obliterated. In connection with
the primary optic vesicle are developed the retina from the
invaginated portion, and the pigmentary portion of the
choroid in connection with the outer part (fig. 236). In
the secondary optic vesicle the vitreous humour is formed.
The outer walls of the eyeball, the sclerotic and cornea,
‘are developed from the tissues immediately around those
which have been just described.

The iris is formed rather late, as a circular septum pro-
jecting inwards, from the fore part of the choroid, between
the lens and the cornea. In the eye of the foetus of Mam-
malia, the pupil is closed by a delicate membrane, the
membrana pupillaris, which forms the front portion. of a
highly vascular membrane that, in the foetus, surrounds

Fig. 238.*

WwW

* Fig. 238. Blood-vessels, of the capsulo-pupillary membrane of a
new-born kitten, magnified (from K@lliker). The drawing is takenfrom
a preparation injected by Tiersch, and shows in the central part the
convergence of the net-work of vessels in the pupillary membrane.

i, e
- —_—

a

DEVELOPMENT OF THE ALIMENTARY CANAL. 773

is supplied with blood by a branch of the arteria centralis
retiné, which, passing forwards to the back of the lens,
there subdivides. The membrana capsulo-pupillaris withers
and disappears in the human subject a short time before
birth.

The eyelids of the human subject and mammiferous
animals, like those of birds, are first developed in the form
of a ring. They then extend over the globe of the eye
until they meet and become firmly agglutinated to each
other. But before birth, or in the Carnivora after birth,
they again separate.

The ear likewise, according to Huschke, consists of a
part developed from within, and of one formed externally.
The labyrinth is developed upon the hollow protruded part
of the brain which forms the auditory nerve. It appears
first in the form of an elongated vesicle at the hinder part
of the head of very young embryos above the second
so-named branchial cleft.. From it is developed a second
vesicle, the rudiment of the cochlea, the convolutions of
which are then formed. The semicircular canals are pro-
duced, as diverticula of the vestibule, which terminate by
again communicating with the same cavity. _

The Eustachian tube, the cavity of the tympanum, and
the external auditory passage, are remains of the first
branchial cleft. The membrana tympani divides the cavity
of this cleft into an internal space, the tympanum, and
the external meatus. The mucous membrane of the
mouth, which is prolonged in the form of a diverticulum
through the Eustachian tube into thé tympanum, and the
external cutaneous system, come into relation with each
other at this point; the two membranes being separated
only by the proper membrane of the tympanum.

Development of the Alimentary Canal.

The alimentary canal, the early stage of whose develop -
ment has been already referred to (p. 746), is at first an

774 GENERATION AND DEVELOPMENT.

uniform straight tube, which gradually becomes divided |
into its special parts, stomach, small intestine, and large
intestine (fig. 239). The stomach originally has the same
direction as the rest of the canal; its cardiac extremity
being superior, its pylorus inferior, The changes of
position which the alimentary canal undergoes may be
readily gathered from the accompanying figures.

A B Fig. 239.* ©

|
—— §

The principal glands in connection with the intestinal
canal are the salivary, pancreas, and the liver. In Mam-
malia, each salivary gland first appears as a simple canal
with bud-like processes (fig. 240), lying in a gelatinous
nidus or blastema, and communicating with the cavity of

i
i
{
\
,
¥
a
‘
;

* Fig. 239. Outlines of the form and position of the alimentary canal
in successive stages of its development (from Quain), A, alimentary
canal, &c., in an embryo of four weeks ; B, at six weeks; C, at eight
weeks ; D, at ten weeks; /, the primitive lungs connected with the pharynx;
s, the stomach ; d, duodenum ; #, the small intestine ; 7’, the large ; c, the
ccecum and vermiform appendage ; 7, the rectum ; c/, in A, the cloaca ;
a, in B, the anus distinct from sé, the sinus uro-genitalis; v, the yolk
sac; vz, the vitello-intestinal duct ; w, the urinary bladder and urachus
leading to the allantois ; g, genital ducts.

re)

DEVELOPMENT OF THE LIVER. 775

the mouth. As the development of the gland advances,
the canal becomes more and more ramified, increasing at

Fig. 240.* Fig. 241.+

the expense of the blastema in which it is still enclose
The branches or{fsalivary ducts constitute an independent
system of closed tubes (fig. 241). The pancreas is developed
exactly as the salivary glands.

The liver in the embryo of the bird is developed by the
protrusion, as it were, of a part of the walls of the in-
testinal canal, in the form of two conical hollow branches
which embrace the common venous stem (fig. 242). The
outer part of these cones involves the omphalo-mesenteric
vein, which breaks up in its interior into a plexus of
capillaries, ending in venous trunks for the conveyance of
the blood to the heart. The inner portion of the cones
forms the cellular structure of the organ into which the

* Fig. 240. First appearance of the parotid gland in the embryo of
a sheep.

+ Fig. 241. Lobules of the parotid, with the salivary ducts, in the
embryo of the sheep, at a more advanced stage.

776 GENERATION AND DEVELOPMENT. .

blood-vessels extend, and in which they are, with the ducts,
gradually developed. The gall-bladder is developed as a
diverticulum from the hepatic duct.

Fig. 242.*

“)

Development of the Respiratory Apparatus.
The lungs, at their first-development, appear as small
tubercles, or diverticula from the abdominal surface of the

Eig. 243.7

* Fig. 242. Rudiments of the liver on the intestine of a chick at the
fifth day ofincubation. 1, heart; 2, intestine; 3, diverticulum of the
intestine on which the liver (4) is developed ; 5, part of the mucous
layer of the germinal membrane.

t+ Fig. 243, illustrates the development of the respiratory organs. <A,
is the esophagus of a chick on the fourth day of incubation, with the
rudiments of the trachea on the lung of the left side, viewed laterally :
1, the inferior wall of the cesophagus; 2, the upper wall of the same
tube ; 3, the rudimentary lung; 4, the stomach. 8, is the same object
seen from below, so that both lungsare visible. c, shows the tongue and
respiratory organs of the embryo of a horse : 1, the tongue ; 2, the larynx;
3, the trachea ; 4, the lungs viewed from the upper side. After Rathke.

7 a

i ee a) eee

THE WOLFFIAN BODIES. a yi

cesophagus. They are united at the anterior part of their
circumference ; and here a pedicle is formed which becomes
elongated into the trachea (see fig. 243, a, 8). Soon after-
wards, the lung is seen to consist of a mass of cecal tubes -
issuing from the branches of the trachea. (Fig. 243, c).
The diaphragm is early developed. |

The Wolffian Bodies, Urinary Apparatus, and
, _ Sexual Organs.

The Wolffian bodies are organs peculiar to the em-
bryonic state, and may be regarded as temporary, rather
than rudimental, kidneys; for although they seem to dis-
charge the functions of these latter organs, they are not
developed into them. They probably bear the same relation
to the persistent kidneys that the branchize of Amphibia
do to the lungs which succeed them.

In Mammalia, the Wolffian bodies (fig.244,W.) are bean-

shaped, and are composed of transverse ceecal canals, united

by an excretory duct (w) which leads from the lower ex-
tremity of the organ to the sinus-urogenitalis of the footus
(fig. 244, ug). The kidneys (r) and supra-renal capsules (sr)
are developed behind them: Their size is at first so great
that they entirely conceal the kidneys; but in proportion
as the latter bodies increase in size, they grow relatively
smaller, and come to be placed more inferiorly. At length,
towards the end of foetal life, only an atrophied remnant
of them is left. Their ducts, in the male, are ultimately
developed to form the vas deferens and ejaculatory duct of
each side; the vesiculze seminales forming diverticula from
their lower part. In the female, the ducts of the Wolffian
bodies disappear.

The testicles or ovaries are formed independently
at the internal excavated border of these organs; and at

first it is not possible to say which of them—the testicle
or ovary—the new formation is to become. Gradually,
however, the special characters, belonging to one of

778 GENERATION AND DEVELOPMENT.

them are developed; and in either case the organ soon
begins to assume a relatively lower position in the body ;
the ovaries being ultimately placed in the pelvis; while
towards the end of fcetal existence the testicles descend
into the scrotum, the testicle entering the internal
inguinal ring in the seventh month of foetal life, and com-
pleting its descent through the inguinal canal and external
ring into the scrotum by the end of the eighth month. A
pouch of peritoneum, the processus vaginalis, precedes
it in its descent, and ultimately forms the tunica vaginalis
“or serous covering of the organ; the communication
between the tunica vaginalis and the cavity of the perito-
neum being closed only a short time before birth. In its
descent, the testicle or ovary of course retains the blood-
vessels, nerves, and lymphatics, which were supplied to it
while in the lumbar region, and which are compelled to
follow it, so to speak, as it assumes a lower position in the
body. Hence the explanation of the otherwise strange fact
of the origin of these parts at so considerable a distance
from the organ to which they are distributed.

The means by which the descent of the testicles into the
scrotum is effected are not fully and exactly known. It
was formerly believed that a membranous and partly
muscular cord, called the gubernaculum testis, which extends
while the testicle is yet high in the abdomen, from its
lower part, through the abdominal wall (in the situation
of the inguinal canal) to the front of the pubes and
lower part of the scrotum, was the agent by the contraction
of which the descent was effected. Itis now generally
believed, however, that such is not the case; and that the
descent of the testicle and ovary is rather the result of a
general process of development in these and neighbouring
parts, the tendency of which is to produce this change
in the relative position of these organs. In other words,
the descent is not the result of a mere mechanical
action, by which the organ is dragged down to a lower

:

a sie hee le

THE MULLERIAN DUCTS. 779

position, but rather one change out of many which attend
the gradual development and re-arrangement of these
organs. It may be repeated, however, that the details of
the process by which the descent of the testicle into the
scrotum is effected are not accurately known.

The homologue, in the female, of the gubernaculum
testis, is a structure called the round ligament of the uterus,
which extends through the inguinal canal, from the outer
and upper part of the uterus to the subcutaneous tissue in
front of the symphysis pubis.

At a very early stage of foetal life, the efferent Sita of
the Wolffian bodies of the kidneys and of the ovaries: or
testes, open into a receptacle formed by the we r end of
the allantois, or rudimentary bladder; and as this com-
municates with the lower extremity of the intestine, there
is for the time, a common receptacle or cloaca for all these
parts, which opens to the exterior of the body through a
_part corresponding with the future anus. In a short time,
however, the intestinal portion of the cloaca is cut off from
that which belongs to the urinary and generative organs ;
a separate passage or canal to the exterior of the body,
belonging to these parts, being called the sinus wrogenitalis.
Subsequently, this canal is divided, by a process of division
extending from before backwards or from above down-
wards, into a ‘pars urinaria”’ and a “‘pars genitalis.”” The
former, continuous with the urachus (p. 749), is converted
into the urinary bladder.

The Fallopian tubes, the uterus, and the vagina are
developed from two threads of blastema, called the
Miillerian ducts (fig. 244, m), which appear in front of the
Wolffian bodies at about the time that these begin to
change their relative position to neighbouring parts, and
to decrease in size. The two Miillerian ducts are united
below into a single cord, called the genital cord, and, from
this are developed the vagina, as well as the cervix and
the lower portion of the body of the uterus; while the

780 «GENERATION AND DEVELOPMENT.

-

ununited portion of the duct on each side forms the upper
part of the uterus, and the Fallopian tube. In certain
cases of arrested or abnormal development, these portions

Fig. 244.*

of the Miillerian ducts may not become fused together at
their lower extremities, and there is left a cleft or horned
condition of the upper part of the uterus, resembling a con-
dition which is permanent in certain of the lower animals.

In the male, the Millerian ducts have no special
function, and are but slightly developed: the small prosta-
tic pouch, or sinus pocularis, forms the atrophied remnant

* Fig. 244. Diagram of the Wolffian bodies, Millerian ducts and
adjacent parts previous to sexual distinction, as seen from before (from
Quain). sr, the supra-renal bodies ; 7, the kidneys ; of, common blas-
tema of ovaries or testicles ; W, Wolffian bodies; w, Wolffian ducts ;
m, m, Miillerian duct; ge, genital cord; wg, sinus urogenitalis ; i,
intestine ; cl, cloaca.

Ea

THE EXTERNAL PARTS OF GENERATION. 781

of the genital cord, and is, of course, tlierefore, the homo-
logue, in the male, of the vagina and uterus in the female.

Fig. 245."

The external parts of generation are at first the same in
both sexes. The opening of the genito-urinary apparatus

* Fig. 245. Urinary and generative organs of a human femaleembryo,
measuring 34 inches in length. A, general view of these parts ; 1, supra-

~ renal capsules; 2, kidneys; 3, ovary ; 4, Fallopian tube; 5, uterus;

6, intestine ; 7, the bladder. 3, bladder and generative organs of the
same embryo viewed from the side ; 1, the urinary bladder (at the upper
part is a portion of the urachus); 2, urethra; 3, uterus, (with two
cornua) ; 4, vagina; 5, part as yet common to the vagina and urethra ;
6, common orifice of the urinary and generative organs ; 7, the clitoris.
c, internal generative organs of the same embryo; 1, the uterus; 2,
the round ligaments ; 3, the Fallopian tubes (formed by the Miillerian
ducts) ; 4, the ovaries; 5, the remains of the Wolffian bodies. D, ex-
ternal generative organs of the same embryo; 1, the labia majora ;
2, the nymphe ; 3, the clitoris. After Miller.

SS

78 2 GENERATION AND DEVELOPMENT.

is, in both sexes, bounded by two folds of skin, whilst in
front of it there is formed a penis-like body surmounted
by a glans, and cleft or furrowed along its under surface.
The borders of the furrow diverge posteriorly, running at
the sides of the genito-urinary orifice internally to the
cutaneous folds just mentioned (see fig.245,B,D). In the
female, this body becoming retracted, forms the clitoris,
and the margins of the furrow on its under surface are
converted into the nymphe, or labia minora, the labia
majora pudende being constituted by the great cutaneous
folds. In the male foetus, the margins of the furrow at
the under surface of the penis unite at about the four-
teenth week, and form that part of the urethra which is
included in the penis. The large cutaneous folds form
the scrotum, and at a later period, namely, in the eighth
month of development, receive the testicles, which descend
into them from the abdominal cavity. Sometimes the
urethra is not closed, and the deformity called hypospadias
then results. The appearance of hermaphroditism may,
in these cases, be increased by the retention of the testes
within the abdomen.

The Mammary Glands.

The mammary glands, which may be considered as
organs superadded to the reproductive system in man and
other members of the class (Mammalia) which derives its
name from them, are, in the essential details of their struc-
ture, very similar to other compound glands, as the
pancreas and salivary glands; that is to say, they are
composed of larger divisions or lobes, and these are
again divisible into lobules,—the lobules being composed
of the follicular extremities of ducts, lined by glandular
epithelium. The lobes and lobules are bound together
by areolar tissue ; while, penetrating between the lobes,
and covering the general surface of the gland, with
the exception of the nipple, is a considerable quantity

/
ere. SS -

THE MAMMARY GLANDS. 783

of yellow fat, itself lobulated by sheaths and processes of
tough areolar tissue (fig. 246) connected both with the skin
in front and the gland behind ; the same bond of connec-
tion extending also from the under surface of the gland to

the sheathing connective tissue of the great pectoral muscle
on which it lies, The main ducts of the gland, fifteen to

* Fig. 246. Dissection of the lower half of the female mamma
during the period of lactation (from Luschka. 3.—In the left-hand side
of the dissected part the glandular lobes are exposed and partially un-
ravelled ; and on the right-hand side, the glandular substance has been
removed to show the reticular loculi of the connective tissue in which
the glandular lobules are placed : 1, upper part of the mamillaor nipple ; 2,
areola ; 3, subcutaneous masses of fat ; 4, reticular loculi of the connective
tissue which support the glandular substance and contain the fatty
masses; 5, one of three lactiferous ducts shown passing towards the
mamilla where they open; 6, one of the sinus lactei or reservoirs ;
7, some of the glandular lobules which have been unravelled ; 7’, others
massed together.

784 GENERATION. AND DEVELOPMENT.

twenty in number, called the lactiferous or galactophorous
ducts, are formed by the union of the smaller ducts, and

open by small separate orifices through the nipple. Just

before they enter the base of the nipple, these ducts are
dilated (6, fig. 246); and, during lactation, the period of
active secretion by the gland, they form reservoirs for the
milk, which collects in them and distends them. The walls
of the gland-ducts are formed of areolar and elastic tissue,
and are lined internally by a fine mucous membrane, the
surface of which is covered by squamous or spheroidal
epithelium.

Fig. 247.*

The nipple, which contains the terminations of the
lactiferous ducts, is composed also of areolar tissue, and
contains unstriped muscular fibres. Blood-vessels are also
freely supplied to it, so as to give it a species of erectile
structure. On its surface are very sensitive papille; and
around it is a small area or areola of pink or dark-tinted
skin, on which are to be seen small projections formed by
minute secreting glands. .

Blood-vessels, nerves, and lymphatics are plentifully
supplied to the mammary glands; the calibre of the blood-
vessels, as well as the size of the glands, varying very

* Fig. 247. Globules and molecules of cow’s milk *2°.

lll a a, ia ie

COMPOSITION OF MILK. 785

greatly under certain conditions, especially those of preg-
nancy and lactation.

The secretion of milk, which under ordinary healthy
circumstances only occurs after parturition, if we except
the slight secretion which takes place in the latter months
of pregnancy, is effected by the epithelial cells lining the
ultimate follicles of the mammary gland. The process does
not differ from secretion in glands generally (see p. 404),
and need not here be particularly described.

Under the microscope, milk is found to contain a
number of globules of various sizes (fig. 247), the majority
about +,1,, of an inch in diameter. They are composed of
oily matter, probably coated by a fine layer of albuminous
material, and are called milk-globules ; while, accompanying
these, are numerous minute particles, both oily and albu-
minous, which exhibit ordinary molecular movements. The
milk, which is secreted in the first few days after parturi-
tion, and which is called the colostrum, differs from ordinary
milk in containing a larger quantity of solid matter; and
under the microscope are to be seen certain granular masses
called colostrurt-corpuscles. These, which appear to be small
masses of albuminous and oily matter, are probably secret-
ing cells of the gland, either in a state of fatty degenera-
tion, or, as Dr. Gedge remarks, old cells which. in their
attempts at secretion under the new circumstances of active
need of milk, are filled with oily matter; which, however,
being unable to discharge, they are themselves shed bodily |
to make room for their successors.

The specific gravity of human milk is about 1030. Its
chemical composition has been already mentioned (p. 246).

; a Hy rf 3 4 y eg iallhed
i oe § i iy) vila ; on - - iy a oth

nui <a

. -
fet 1 se We
s ey”

’ '-
a 5 oe?

es - ern fun Vaud tty oft REE Va
f - Ud

re Ladi

ay) b : ; 7

aay) Suir
aa : \ : ey ba ot m ‘ ae
"3 : =|* : ( my me

4 MNS al o% ’ fl) —
* j ? dike ; } '
‘a ¥ 7 a :
al
0a g a +4 ?
1 aS . : a P ¥ ‘ a 4
: $: ‘ 2
a! oe i _ ‘.
,
é~ ‘ STs ‘ $ : ae i Bi
&
.
, J “ ae
. ” +
: ed } 6. 407 Ls ’ oe att
jar
a ; He 7 : ees ; ‘ P. 35
7 +
: - e - 7 *
a= , ie . ich
’ : v6 A é ; = » “peeks «
A .
: L al
in a y " ~, »
s « -, ’
. LP ,

ae ee
me Ate EP ASS bs Mm te are >t ATA. ote

;
Ph ¢
‘ 3 ‘
“f ’
=?
ely 3 F
Nei: « ae:
be (s
.
; . -
ae -
*
- —. t

=

* .

’
’ ¢
. ‘
id .
> oS Pa

ee

——=-

INDEX.

—p-—-

A.

Abdominal muscles, action of in
respiration, 199.
type of respiration, 198.

Aberration,
chromatic, 649.
spherical, 648.

Absorbents. See Lymphatics.

Absorption, 347.
by blood-vessels, 367.
of gases by blood, 371.
by lacteal vessels, 309, 363.
by lymphatics, 364.
of oxygen by lungs, 215.
process of by osmosis, 368.

' purposes of, 347.
rapidity of, 371.
from rectum, rapidity of, 372.
by the skin, 437.
from stomach, preparation of food

for, 285.
See Chyle, Lymph, Lymphatics,
Lacteals.

Accessory nerve, 564.
distribution of, 7,
roots of, 565.

Accidental elements in human body,

19.

Accidents, involuntary movements
in, 506.

Acetic acid in gastric fluid, 275.

Acids, strong, prevent coagulation, 68,

Acini of secreting glands, 403.
Adaptation of eye to distances, 649.
Adenoid tissue. See Retiform Tis-

sue.
Adipose tissue, 38.
situations of, 7.
structure of, 7b.
See Fat.
Afferent
arteries of kidney, 444.

Afferent
lymphatics, 356.
nerve-fibres, 475.

After-birth, 757.

After-sensations,
of taste, 705.
of touch, 711.
of vision, 659.

Age,

in relation to blood, 83.
to capacity of chest, 203.
to excretion of urea, 454.
to exhalation of carbonic acid,

211.
to heat of body, 232.
to mental faculties, 535.
to pulse, 124.
to respiration, 203.
to voice, 616.

Aggregated glands, 403.’ .

Agminate glands, 301.

Air,
atmospheric, composition of, 210.
changes by breathing, 210.
favours coagulation of blood, 66.
quantity breathed, 201.
states of influencing production of

carbonic acid, 213, 214.
transmission of sonorous vibra-
tions through, 683.
in tympanum, necessary for hear-
ing, 685.
undulations of, conducted by ex-
ternal ear, 680.
by tympanum, 684.

Air-cells, 191.

Air-tubes. See Bronchi.

Albinoes, imperfect vision in, 638.

Albumen,
action of gastric fluid on, 284.
characters of, 13.
chemical composition of, 15.
coagulated, properties of, 13.

3 5

788 _ INDEX.

Albumen, continued.
coating oily matter, 359.
relation to fibrin, 14.
tissues and secretion in which it
exists, 13.
of blood, 8o.
uses of, 96.
vegetable, 249.
Albuminose, 285.
action of liver on, 332.
Albuminous substances, 11.
absorption of, 339.
action of gastric fluid on, 284, 339.
of liver on, 285.
of pancreas on, 314, 339.
Alcoholic drinks, effect on respira-
tory changes, 214.
Aliments. See Food. '
Alimentary canal, development of,
773.SeeStomach, Intestines, etc.
Alkalies, caustic, prevent coagula-
tion, 68.
Alkaline and earthy salts, influence
of on coagulation, 67.
Allantois, 747, 748.
Aluminium, an accidental element
‘ in tissues, 18.
Ameeba, 78.
Ameceboid movements of white cor-
puscles, 78.
Amaurosis,
action of iris in, 540.
after injury of the fifth nerve, 550.
Ammonia, in blood, 83.
cyanate of, identical with urea,

453+
exhaled from lungs, 218.
from skin, 434.
urate of, 457.
Amnion, 747.
Ampulla, 676.
Amputation, sensations after, 48o.
Amzylaceous principles,
action of gastric fluid on, 286.
of pancreas and intestinal
glands on, 312, 339.
of saliva on, 262.
Amyloid substance in liver, 333. «
Amyloids, 245.
Anastomoses of muscular fibres of
heart, 586.
of nerves, 470.
of veins, 171.
in erectile tissues, 18 .

Anatomical elements of humam

body, 19-209.
Angle, optical, 655.
Angulus opticus seu visorius, 655.
Ani sphincter. See Sphincter.
Animal fats, ro,

food, digestion of, 283.

in relation to urea, 454.

in relation to uric acid, 456.

in relation to reaction of urine,

448.
heat, 231. See Heat and Tempe-
rature.
life, muscles of, 583.
nervous system of, 464.
starch, 334.
Animals, their distinction from
plants, 4.
Anterior pyramids, 510,
roots of spinal nerves, 494.
Antihelix, 671.
Antitragus, 671.
Anus, 309.

Aorta, 103.

development of, 765.
elasticity of, 135.
pressure of blood in, 154.
valves of, 108.
action of, 115.
Apnea,
force of inspiratory efforts in, 206.
See Asphyxia.
Apoplexy, effects of, 533.
with cross paralysis, 513.
Appendices epiploic, 309.
Appendix vermiformis, 309.
Aqueeductus,
cochles, 677.
vestibuli, 676.
Aqueous humour, 643.
Arches, visceral, 761.
Area germinativa, 743.
pellucida, 743.
vasculosa, 750.
Areola of nipple, 784.
Areolar tissue, 35.
functions of, 37.
situations where found, 35.
Arteries, 100, 133.
calibre of, how regulated, 437,
I4I.
coats of, 133.
muscular contraction of, 138.
effect of cold on, 138, 139.

ee ee a

INDEX.

Arteries, continued.
effect of division, 138.
of electro-magnetism, 140.
elasticity of, 135.
purposes of, 7d.
elongation and dilatation in the
pulse, 144.
force.of blood in, 154.
muscularity of, 133.
evidence of, 138.
governed by nervous system,
142, 575.
purpose of, 141.
nerves of, 142.
office of, 134.
pulse in, 143. See Pulse.
structure of, 133.
distinctions in large and small
arteries, 133.
systemic, 103.
velocity of blood in, 155.
Articular cartilage, 41. !
Articulate sounds, classification of,
619. . See Vowels and Conso-
nants. ,
Artificial digestive fluid, 278.
Arytenoid cartilages, 608.
effect of approximation, 613.
movements of, 608.
muscle, 608, 609.
Asphyxia, 227.
cause of death in, 228.
experiments on, 227.
essential cause of, 231.
Assimilation or maintenance,
of blood, 93.
nutritive, 374.
Atmospheric air. See Air.
pressure in relation to respiration,
194.
Atrophy,
from deficient blood, 334.
from diseased nerves, 387.
Attention, influence of,
on sensations, 628.
on special senses, 658.
Auditory canal, 672.
function of, 680.
Auditory nerve, 679.
distribution of, 679, 690.
effects of irritation of, 697.
fibres of, 475.
sensibility of, 692.
Auricle of ear, 671.,

789
Auricles of heart, 102,

action of, 1009.

capacity of, 128.

development of, 765.

dilatation of, 112. .

force of contraction of, 127.
Axis-cylinder, of nerve-fibre, 467.
Azote. Sce Nitrogen.
Azotized principles, 11.

B.

Barytone voice, 615.
Basement-membrane,
of mucous membranes, 400.
of secreting membranes, 395.
Bass voice, 614.
Benzoic acid, relation to hippuric
acid, 458.
Bicuspid valve, 105.
Bile, 322.
‘antiseptic power of, 331.
colouring matter of, 323.
colouring serous secretions, 397. °
composition of, 322.
elementary, 325.
digestive properties of, 330.
excrementitious, 327.
fat made capable of absorption by,

330-
functions of in digestion, 330.
mixture with chyme, 338.
mucus in, 324.
a natural purgative, 331.
process of secretion of, 326.
purposes of, 327.
in relation to animal heat, 329.
quantity secreted, 327.
re-absorption of, 328, 331.
saline constituents of, 324.
secretion and flow of, 326.
secretion of in foetus, 327.
tests for, 325.
Bilin, 323.
re-absorption of, 328.
Biliverdin and Bilifulvin, 324.
Bipolar nerve-corpuscles, 474.
Birds, their high temperature, 235.
Birth, 1.
Bladder, urinary.
Bladder.
Blastema, 20.
Blastodermic membrane, 742.
Bleeding, effects of on blood, 84.

See Urinary

79°

Blood, 56—98.

adaptation of to tissues, 383.

adequate supply necessary for nu-
trition, 384.

albumen. of, So.
use of, 95.

alteration of by disease, 94.

ammonia in, 83.

animal poisons, how affected by,

3°4-
arterial and venous, differences
between, 85, 89, 219.
assimilation of, 94.
casein in, 83.
changes in by respiration, 219.
chemical composition of, 68.
circulation of, 99. See Circulation.
coagulation of, 60—65.
circumstances influencing, 66.
colour of, 56.
changed by respiration, 219.
differences in, 85.
colouring matters in, $3.
colouring matter, relation to that
of bile, 323.
compared with lymph and
chyle, 357.
composition of, chemical, 68.
physical, 56.
variations in, 83—89.
conditions necessary to nutrition,

383.
corpuscles or cells of, 69—78. See
Blood-corpuscles.

red, 71.

white, 76.
creatin and creatinin in, 82.
crystals of, 74.
development of, 90.

from lymph or chyle, 93.
exposure to air in lungs, 193.
extractive matters of, 82.
fatty matters in, 81.

use of, 97.
fibrin of, 81.

separation of, 14, 65.

use of, 96.
force of in arteries, 155.
formation of in‘ liver, 92.

in spleen, 411.
gases in, 89.

changed by respiration, 220.
of pees and mesenteric veins,

7°

INDEX.

Blood, continued.
globulin of, 74.
glucose or grape-sugar in, 83.
"ebe? and maintenance of, 95.
eematin or cruorin of, 76.
~ hepatic, characters of, 88.
hippuric acid in, 83.
inorganic constituents of, $2.
lactic acid in, $3.
menstrual, 57, 727. ;
molecules or granules in, 78.
movement of, in capillaries, 162.
in lungs, 209.
odoriferous matters in, 83.
odour or halitus of, 57.
portal, characters of, 88.
purification of by liver, 329.
quantity of, 58.
re-absorption of bile into, 328.
reaction of, 57. -
relation of to lymph, 361.
to secretions, 401, 404, 407.
of renal vein, 89.
saline constituents of, 82.
uses of, 97.
serum of, 78.
compared with secretion of se-
rous membrane, 397.
specific gravity of, 57.
splenic, characters of, 88.
structural composition of, 56.
supply of, adapted to each part,
143.
to brain, 181.
necessary for nutrition, 384.
necessary to secretion, 407.
temperature of, 57.
urea in, 83.
uric acid in, 2.
uses of, 95.
variations of in different circum-
stances, $3.
in different parts of body, 84.
water in, 79.
Blood-corpuscles, red, characters of,
6

9.
chemical composition of, 74.
development of, go—92, 381.
in liver, 92.
in spleen, 412.
disintegration and removal of,

414.
diversities of, 72. — :
movement of in capillaries, 163.

INDEX.

Blood-corpuscles, red, continwed.
sinking of, 61.
tendency to adhere, 62, 71.
uses of, 98.

Blood-corpuscles, white, 76.
amceboid movements of, 78.
formation of in spleen, 412.

Blood-crystals, 74.

Blood-vessels,
absorption by, 367-373.

circumstances influencing, 372.
difference from lymphatic ab-
sorption, 367
osmotic character of, 368, 370.
rapidity of, 371.
area of, 162.
communication with lymphatics,

352.
development of, 763.
influence of nervous system on,

575+
of placenta, 752.
relation to secretion, 407.
share in nutrition, 383.

Bone, 45.
canaliculi of, 47.

_ cancellous structure of, 45.
composition of, 7b.
development of, 49.

Haversian canals of, 48.
lacune of, 47.

lamelle of, 48.
periosteum of, 46.
structure of, 45.

Bone-earth, composition of, 18.

Bones or ossicles of ear, 674.

Bones, growth of, 375.
nutrition of, 382.

Boys, voice of, 615.

Brain. See Cerebellum, Cerebrum,

Pons, etc.
capillaries of, 159.
circulation of blood in, 180.
development of, 743, 773-
disease of, with atrophy, 384.
influence on heart’s action, 125.
quantity of blood in, 182.

Breathing-air, 201.

Breathing. See Respiration.

Bronchi, arrangement and structure

of, 189.
muscularity of, 207.
Bronchial arteries and veins, 209.
Brunn’s glands, 305.

791

Buccinator muscle, nervous supply

or, 554 .
Buffy coat, formation of, 62, 73.
Bulbus arteriosus, 766.
Burse mucose, 396.

Cs

Cxcum, 311.
changes of food in, 341.
Calcium, salts of, in human body,
8

18.
Caleuli, biliary, containing chole-
sterin, II.
containing copper, 324.
Calculus, radiation St sensation
from, 486, 499.
Calorifacient food, 248.
Calyces of the kidney, 441.
Calyciform papille of tongue, 701.
Canal, alimentary. See Stomach,
Intestine, ete.
external auditory, 671.
function of, 680.
oral, 620.
of spinal cord, 493.
spiral, of cochlea, 676.
Canaliculi of bone, 47.
Canals, Haversian, 48.
portal, 316.
semicircular, 676.
function of, 689.
Cancellous texture of bone, 45.
Capacity of chest, vital, 202.
how increased or diminished, 195

— 199.
of heart, 125.
Capillaries, 100, 155.
circulation in, 160.
rate of, 162.
contraction of, 164.
development of, 764.
diameter of, 156.
influence of on circulation, 166.
lymphatic, 349.
network of, 157.
number of, 159.
passage of corpuscles through
walls of, 164.
resistance to flow of blood in, 161.
still layer in, 163.
structure of, 156.
systemic, 103.
of lungs, 193, 209.

4

792

Capillaries, continued.
of muscle, 586.
of stomach, 271.
Capsule of Glisson, 316. —
Capsules, Malpighian, 443.
Carbon, union of with oxygen, pro-
ducing heat, 236.
Carbonic acid in atmosphere, 210.
in blood, 87, 89, 219.
effect of in producing asphyxia,

231.
exhaled from skin, 434.
increase of in breathed air, 211.
in lungs, 208.
in relation to heat of body, 236.
Cardiac orifice, action of, 237.
sphincter of, 223.
relaxation in vomiting, 290.
Cardiac branches of pneumogastric
nerve, 558.
Cardiograph, 123.
Carnivorous animals, food of, 246.
sense of smell in, 634.
Cartilage, 41. 5
articular, 43.
cellular, 42.
chondrin obtained from, 11.
elastic, 41.
fibrous, 43. See Fibro-cartilage,
hyaline, 42.
matrix of, 7b.
ossification in, 49.
perichondrium of, 42.
permanent, 41.
structure of, 2b.
temporary, 41, 43.
uses of, 44.
varieties of, 41.
Cartilage of external ear, use in
hearing, 682.
Cartilages of larynx, 607.
of ribs, elasticity of, 198.
Casein in blood, 83.
Catalytic process, 279.
Cauda equina, 490.
Caudate ganglion-corpuscles, 473.
Cells, primary or elementary,
definition of, 25.
contents of, 26.
shape of, ib.
structure of, 25.
blood, 69. See Blood-corpuscles.
cartilage, 41.
embryonic, 90,

INDEX.

Cells, continued.
epithelium, 29-34. See Epithe-
lium.

of glands, 31, 404.
action of in secretion, 407.
lacunar of bone, 47.
mastoid, 673.
nerves ending in, 471.
olfactory, 632.
pigment, 40,
of stomach, 267.
Cellular cartilage, 42.
Cellular tissue, 35. See <Areolar
sue,
Cement of teeth, 51, 53.
Centres, nervous. See Nervous
Centres.
of ossification, 49.
Centrifugal nerve-fibres, 475.
Centripetal nerve-fibres, 7b,
Cerebellum, 524.
co-ordinate function of, 526.
cross action of, 530.
effects of injury of Grura, 7d.
of removal of, 527.
functions of, 526.
in relation to sensation, 7b.
to motion, 7b.
to muscular sense, 528.
to sexual passion, 70.
structure of, 524. . 7
Cerebral circulation, 180.
ganglia, function of, 521.
_ hemispheres, See Cerebrum.
Cerebral nerves, 538.
arrangement of, <b.

third, 539. ’
effects of irritation and injury
of, 2b.
relation of to iris, 540. ;
fourth, 541.
fifth, 543. a
a conductor of reflex impres-
sions, 546. mS

distribution of, 543, 544.
effect of division of, 387, 547.
influence of on iris, 546.

on muscles of mastication,

on muscular movements, 546.
on organs of special sense,
’ S47, 55@ oO ey
relation of to nutrition, 548.
resemblancetospinalnerves, 54 3

at

INDEX.

Cerebral nerves, continued.
sensitive function of greater
division of, 545.
sixth, 541. ;
communication of, with sym-
. pathetic, 7d.
seventh. See Auditory Nerve and
Facial Nerve.
eighth. See Glosso-pharyngeal,
Pneumogastric, and Spinal Ac-
cessory Nerves.
ninth, 555.
ni a pid nervous system, 463,
4
influence on organic life, 577.
See Brain, Spinal Cord, etc.
Cerebro-spinal fluid, relation to cir-
culation, 182.
Cerebrum, its structure, 531.
convolutions of, 532.
crura of, 518.
development of, 770.
effects of injury of, 533.
functions of, 7b.
in relation to speech, 536.
relation to mental faculties, 534.
Cerumen, or ear-wax, 427, 673.
Chalk-stones, 456.
Chambers of eye, 643.
Charcoal, absorption of, 373.
oo actions. how perceived,
628.
composition of the human body, 7.
distinctions between animals and
vegetables, 4.
sources of heat in the body, 236.
_ stimuli, action of nerves excited
by, 477. |
Chest, its capacity, 201.
contents of, 99, 195.
contraction of in expiration, 198.
enlargement ofin inspiration, 195.
Chest-notes, 617.
Children, respiration in, 198.
Chlorine, action onnegro’sskin, 439.
in human body, 17
in urine, 462.
Chloroform, effects of, 517.
Cholesterin, properties of, 11.
in bile, 323.
in blood, 81.
Chondrin, properties of, 11.
Chorda dorsalis, 744.
Chorda tympani, 550.

793

Chorde tendinex, 106.
action of, 114.
Choroin, 751.
villi of, 7b.
Choroid coat of eye, 636, 637.
use of pigment of, 637.
Chromatic aberration, 649.
Chyle, 349, 357.
absorption of, 363.
analysis of, 361.
bile essential to, 330.
coagulation of, 359.
compared with lymph, 36r1.
corpuscles of, 360. See Chyle-
«corpuscles.
course of, 348.
fibrin of, 359.
forces propelling, 353.
molecular base of, 358.
properties of, 7d.
quantity found, 362.
relation of to blood, 7.
Chyle-corpuscles, 360.
evelopment into blood-corpus-
cles, 93, 360.
Chyme, 280, 337.
absorption of digested parts of,
338.
changes of in intestines, 7.
Cicatrix, effect of nutrition on, 389.
Cilia, 33, 578. ;
Ciliary epithelium, 33.
of air passages, 189.
function of, 34.
Ciliary motion, 33, 578.
action of in bronchial tubes, 209.
independent of nervous system,
579.
nature of, ib.
Ciliary muscle, 645.
action of in adaptation to dis-
tances, 650.
Ciliary processes, 638.
Circulation of blood, 99.
action of heart on, 109-119.
agents concerned in, 173.
in arteries, 134.
force of, 152.
velocity of, 155.
in brain, 180.
in capillaries, 160.
rate of, 162.
course of, 100, 103. __
in erectile structure, 183.

794

Circulation of blood, continued.
in foetus, 767.
forces acting in, 102, 173.
influence of respiration on, 7b.
pee of in different parts,
180.

portal, 102.
pulmonary, 101, 208.
systemic, IOI, 103.
in veins, 167.
affected by muscular pressure,
170.
by respiratory movements,

174.
velocity of, 175.

velocity of, 176.
Cireulus venosus, 750.
Circumferential fibro-cartilages, 44.
Circumvallate papille, 701.
Cleaving of yelk, process of, 740.
Cleft, ocular, 772.
Clefts, visceral, 761.
Climate, relation of to heat of body,

234.
Clitoris, 717.
development of, 781.
an erectile structure, 183.
Clot or coagulum of blood, 60.
contraction of, 61. See Coagu-
tion.
of chyle, 359.
Coagulation,
of albumen, 13.
of bloced, 60.
conditions affecting, 66.
influence of respiration on, 219.
theories of, 63.
of chyle, 359.
of lymph, 361.
Cochlea of the ear, 676.
office of, 690.
Cold-blooded animals, 235.
extent of reflexmovementsin, 502.
retention of muscular irritability

m, 592.

Collateral circulation in veins, 171.
Colloids, 369.
Colon, 309.
Colostrum, 785.
Colouring matters, 16.
Colouring matter of bile, 323.

of blood, 74.

of urine, 459.
Colours, optical phenomena of, 659.

INDEX.

Columne carnex, 107.
action of, 111.
Columnar epithelium, 31.
layer of retina, 640.
Columns of medulla oblongata,

509.
Columns of spinal cord, 490.
functions of, 498.
Combined movements, office of cere-
bellum in, 527.
Commissure of spinal cord, 490.
Complemental air, 201.
colours, 660.
Concha, 671.
use of, 680.
Conduction of impressions,
in medulla oblongata, 513.
in or through nerve-centres, 484.
in nerve-fibres, 474.
in spinal cord, 495.
in sympathetic nerve, 572.
Conductors, nerve-fibres as, 474.
Conglomerate glands, 403.
Coni vasculosi, 732.
Conical papille, 7or. |
Conjunctiva, 636.
Connective tissue, 35. See Areolar
Tissue.
corpuscles, 37.
Consonants, 619. *
varieties of, 621.
Contractility,
of arteries, 138.
of bronchial tubes, 207.
muscular tissue, 587.
influence of nerves on, 7.
Contraction,
of coagulated fibrin, 61.
of muscular tissue, mode of, 588.
Contralto voice, 614.
Convoluted glands, 403,
Convolutions, cerebral, 531.
Co-ordination of movements, office
of cerebellum in, 527. °
office of sympathetic ganglia in,

74-
Sie: an accidental element in
~ the body, 19.
in bile, 324.
Cord, spinal. See Spinal Cord.
umbilical, 757.
Cords, tendinous, in heart, 106.
vocal, See Vocal Cords.
Corium, 419, 421.

INDEX.

Cornea, 636, 637.:
action of on rays of light, 642.
nutrition of, 387.
protective function of, 645.
ulceration of, in imperfect nutri-
tion, 387.
after injury of fifth nerve, 2.,

547-
Corpora Arantii, 108, 119.
geniculata, 520.
quadrigemina, 7b.
their function, 521.
striata, 520.
their function, 521.

Corpus callosum, office of, 536.
cavernosum penis, 183.
dentatum, 525.
luteum, 727.

of human female, 728.
of mammalian animals, 7d.
of menstruation and pregnancy
compared, 731.
spongiosum urethre, 183.
Corpuscles of blood. See Blood-
corpuscles,
of chyle, 359.
of connective tissue, 37.

— of lymph, 358.
nerve. See Nerve-corpuscles.
Pacinian, 471.

Cortical substance of kidney, 440.
of lymphatic glands, 355.

Corti’s rods, 678.
office of, 692.

Costal types of respiration, 198.

Coughing, influence on circulation

in veins, 174.
mechanism of, 222.
sensation in larynx before, 486.

Cowper’s glands, 731.
office uncertain, 737.

Cracked voice, 616.

Cramp, 484, 495.

Cranium, development of, 760.

Crassamentum, 60.

Creatin and Creatinin, 16.
in blood, 82.
in urine, 460.

Crico-arytenoid muscles, 609, 610.

Cricoid cartilages, 607.

Cross paralysis, 513.

Crura cerebelli, 524.
effect of dividing, 530.

of irritating, 526.

795

Crura, continued.
cerebri, 518.
effects of dividing, 520.
their office, 520.
Crusta petrosa, 51, 53.
Cryptogamic plants, movements of
spores of, 5.
Crystalline lens, 643.
- inrelation to vision at different
distances, 650.
masses in ear, 690.
Crystalloids, 369.
Crystals, growth of, 2.
in blood, 74.
Cupped appearance of blood-clot, 62.
Curves of arteries, 144.
Cuticle. See Epidermis, Epithe-
lium.
_of hair, 429.
thickening of, 391.
Cutis anserina, 583.
vera, 419, 421.
Cyanate of ammonia, 453.

- Cylindrical epithelium, 33.

Cystic duct, 314, 326.
Cystin in urine, 462.
Cytoblasts, 23.
in 5 and growing parts,
382.

D.

Day, time of, influence on exhala-
tion of carbonic acid, 214.
Decapitated animals, reflex acts in,

501.
Decay of blood-corpuscles, 93.
Decidua, 754.
reflexa, 2).
serotina, 7.
vera, 7.
Decomposition, tendency of animal
compounds to, Lo.
Decussation of fibres in medulla
oblongata, 511, 512.
in spinal cord, 499.
of optic nerves, 668.
Defzecation, mechanism of, 223.
influence of spinal cord on, 508.
Degeneration of tooth-fangs, 380.
Deglutition, 263.
connection with medulla oblon-
gata, 516.
a reflex act, 500.

796

Deglutition, continued.
relation of pneumogastric nerve
ae ete.
Dental groove, primitive, 54.
Dentine, 51.
Depressor nerve, 563.
Derma, 419.
Descendens noni nerve, 565.
Development, 3, 739.
relation to growth, 390.
of organs, 758.
of alimentary canal, 773.
of blood, 90.
of bone, 49.
of embryo, 739, ¢ s.
of extremities, 762.
of face and visceral arches, 760.
of heart and vessels, 763.
of nervous system, 770.
of organs of sense, 7.
of respiratory apparatus, 776.
of teeth, 54.
of vascular system, 763.
of bie column and cranium,
75

of Wolffian bodies, urinary appa-.

ratus and sexual organs, 777.
spices formation of in digestion,
286.
Diabetes, 336, 452.
Diaphragm, 99.
action of on abdominal viscera,
221.
in inspiration, 195, 196.
in various respiratory acts, 220,
225.
in vomiting, 289, 290.
Dicrotous pulse, 151.
Diet, influence of on blood, 84.
Diffusion of gases in respiration, 208.
of impressions, 486.
Digestion, general nature of, 245.
of food in the intestines, 297.
of food in the stomach, 265, 276.
influence of nervous system on,
291.
of stomach after death, 294.
See Gastric Fluid, Food, Stomach.
Digestive fluid. See Gastric Fluid.
artificial, 278,
tract of mucous membrane, 398.
Direction of sounds, perception of,

693.
of vision, 656.

INDEX.

Discus proligerus, 719.
Disease in relation to assimilation
and nutrition, 384.
in relation to heat of body, 234.
Diseased parts, assimilation in, 389.
Diseases, alteration of blood pro-
duced by, 384.
maintenance of alterations by,

389.
reflex acts in, 507.
Distance, adaptation of eye to, 649—
652.
of sounds, how judged of, 694.
Distinctness of vision, how secured,

647.
Dorsal lamine, 743, 760.
Dorsum of tongue,. 700,
Double hearing, 695.
vision, 664.
Dreams, phenomena of, 535.
Dropsy, serous fluid of, contains
albumen, 13.
Drowning, cause of death in, 229.
Duct, cystic, 314, 326.
hepatic, 314, 320.
thoracic, 349, 358.
vitelline, 745.
Ductless glands, 410.
Ducts of glands, arrangement of,
401.
contraction of, 407.
lactiferous, 784.
Ductus arteriosus, 769.
venosus, 767.
closure of, 7609. . '
Duodenum, 297.
ee of impressions, on retina,
59-
Duverney’s glands, 718.
Dysphagia, absorption from nutri-
tive baths in, 438.

Ei

Far, 671.
bones or ossicles of, 674.
function of, 685.
development of, 773.
external, 671.
function of, 680.
internal, 675. :
function of, 689.
middle, 673.
function of, 683.

INDEX,

Ectopia vesice, observations on, 447.
Efferent nerve-fibres, 475. es
lymphatics, 356.
vessels of kidney, 444. .
Eggs as articles of food, 247.
Eighth cerebral nerve, 553.
Elastic cartilage, 41.
‘coat of arteries, 133.
fibres, 36. .
recoil of chest and lungs, 199.
tissue, in arteries, 133.
in bronchi, 188.
tissues, heat developed in, 233.
Elasticity, .
of arteries, 135.
employed in expiration, 198.
Electricity, effect on nerves, 477.
Electro-magnetism,
effect on arteries, 140.
on rigor mortis, 593.
on voluntary muscles, 591.
Elementary substances in the human
body, 7.
accidental, 19.
Embryo. See Development and

cetus.
formation of blood in, go.
Emission of semen a reflex act, 505.
Emotions, connection of with cere-
bral hemispheres, 533-
Enamel of teeth, 51, 53.
End-bulbs, 425, 471.
End-plates, motorial, 471.
Endolymph, 676, 678.
function of, 689.
Endosmometer, 368.
Epidermis, 30, 419.
development, etc., of, 380.
functions of, 426.
hinders absorption, 372.
nutrition of, 385.
pigment of, 420.
‘ relation to sensibility, 426.
structure of, 21, 30, 419.
thickening of, 420.
Epididymis, 731.
Epiglottis, .

action in swallowing, 264.

influence of on voice, 612.
Epilepsy, reflex acts in, 488.
Epithelium, 29.

ciliated, 34.

parts occupied by, % See
Ciliary Motion.

797

Epithelium, continued.
cylindrical or columnar, 31.
glandular, 7.
relation to gland cells, 31, 401.
spheroidal, 30.
squamous or tesselated, 30.
uses of, 34.
of air-cells, 192.
‘of arteries, 133.
of bronchi, 189.
of bronchial tubes, 190.
of Fallopian tubes, 715.
of Graafian follicles, 718.
of hepatic duct, 320.
of intestinal villi, 306.
absorption by, 338, 364.
of Lieberkiihn’s glands, 299.
of mucous membranes, 398.
of olfactory region, 631.
of salivary glands, 258.
of secreting glands, 4o1.
of serous membranes, 395.
of the tongue, 702.
of tubular glands of stomach, 268.
of tympanum, 673.
of urine-tubes, 441.
in bile, 324.
in mucus, I5.
in saliva, 258.
in urine, 459.
Erect position of objects, perception
of, 653.
se o> structures, circulation in,
183.
Erection, 7b.
cause of, 184.
influence of muscular tissue in,
ib. :
of penis, connection of with cere-
bellum, 528.
a reflex act, 505.
Eunuchs, voice of, 616.
Eustachian tube, ¥/
development of, 773.
function of, 688.
Excito-motorandsensori-motoracts,
504, note.
Excreta in relation to muscular ac-
tion, 602.
Excretin, 342.
Excretoleic acid, 342.
Excretion,
direct and indirect, of bile, 329.
general nature of, 394.

798

Excretory organs, influence of on
blood, 95, 186.
Exercise,
effects of on muscles, 375.
on nervous tissue, 376.
on production of carbonic acid,
215.
on temperature of body, 242.
on venous circulation, 172.
undue, increased. growth from,

3°7-
Expansion and contraction of chest,
195-199.
Expiration, 195.
influence of on circulation, 174.
mechanism of, 198.
muscles concerned in, 2.
relative duration of, 200.
Expired air, properties of, 210.
Expression, loss of, in paralysis of
facial nerve, 551.
Expulsive actions, mechanism of,
223.
Extractive matters,
in blood, 82.
in urine, 459.
_ Extremities, development of, 762.
Eye, 636, e. s.
adaptation to vision at different
distances, 649-652.
capillary vessels of, 159.
development of, 770.
effect 43 of injury of facial nerve,

of fifth nerve, 387, 548.
movements of, 542.
nerves, supplying muscles of,
539-543

optical eatin of, 645.
refracting media of, 642.
structure of, 636.

Eyelids, development of, 773.

Eyes, simultaneous action” of in

vision, 664.

F.

Face, development of, 760.
oe: of injury of seventh nerve

n, 552.
‘stinonce of fifth nerve on, 545.
Facial nerve, 550.
effects of paralysis of, 551.
relation of to expression, 552.

INDEX.

Feces, re Se of, 342.-
quantity of, 2b.
result of examination of, 283.
Fallopian tubes, 714.
ciliated epithelium in, 33.
opening into abdomen, 396.
reflex action of, 506.
Falsetto notes, 617.
Fascie, 37.
Fasciculi of muscles, 583.
Fasciculus,
olivary, 512.
teres, 7.
Fasting,
influence on secretion of bile, 326.
saliva during, 259.

at.
action of bile on, 330, 338.
of pancreatie secretion on, 313,

33°-
of small intestine on, 338.
situations where found, 38.
structure “, ib.
uses of, 3
Fatty wii olatile, in blood, 8.
Fatty substances,
compositionand description of, 11.
absorbed by lacteals, 338.
in relation to heat of body, 242.
of bile, 323.
in blood,- 81.
use of, 97.
of chyle, 358.
Female generative organs, 714.
voice, 614.
Fenestra ovalis, 676.
office of, 689.
rotunda, 677.
office of, 689.
Fermentation, digestion compared
h, 279.
echene 16.
Fibre-cells of involuntary muscle,

581.
Fibres of Miiller, 640, 641.
of muscle, involuntary, 581.
erring 583. See Muscular

of nerves. See Nerve-fibres.
various forms of, 28.
Fibrils or filaments, 28.
muscular, 585.
Fibrin in blood, 81.
coagulating principle in, 60.

INDEX.

Fibrin, continued.
use of, 96.
in chyle, 359.
compared with albumen, 14.
formation of, 64.
artificial, 14.
in lymph, 358, 361.
sources and properties, of, 14.
vegetable, 249.
weight in blood includes white
corpuscles, 81.
Fibrinoplastic and _ fibrinogenous
matter, 65.
Fibrinoplastin, 65, 74.
Fibro-cartilage, 41.
white, 44.
yellow, 43.
Fibrinogen, 65.
Field of vision, actual and ideal size
of, 654.
Fifth nerve, See Cerebral
Nerves.
Filaments, 28.
seminal, 734.
Filiform papille of tongue, 700, 701.
Fillet, 512.
Filum terminale, 490, 538.
Fimbrie of Fallopian tube, 715.
Fingers, development of, 762.
Fish, ;
cerebella of, 520.
temperature of, 235.
Fissure of spinal cord, 490.
Fistula, gastric, experiments in
cases of, 272, 274, 277.
Flesh compared with blood, 69.
Fluids, passage of through mem-
branes, 368.
Fluorin in animal body, 17.
Focal distance, 649.
Feetus,
blood of, go.
circulation in, 767.
communication with mother, 755-

543+

757:
feeces of, 327.
office of bile in, 328.
pulse in, 125.
Follicles,
Graafian, 718. Sce Graafian Vesi-
cles.
of hair, 429.
of Lieberkiihn, 299.
Food, 245-254.

799

Food, continued.

action of bile on, 330.
of gastric fluid, 276, 280, 281.
of pancreatic secretion, 313.
of pepsin, mode of, 279.
of saliva, 261-263.
of stomach, 287.

albuminous changes of, 284, 313,

. 339:
amylaceous, changes of, 262, 286,
, 312, 339.
animal, digestion of, 281.
of animals, 246.
calorifacient or respiratory, 248.
of carnivorous animals, 249.
obege of by digestion, chemical,
284.
structural, 7b.
in large intestines, 340.
in mouth, 256.
in small intestines, —340.
in stomach, 280.286 7
classification of, 245.
digestibility of articles of, 283.
value dependent on, 255.
digestion of, in intestines, 297.
in stomach, 265.
eggs, an example of mixed, 247.
fatty elements of, changes of,
313, 330.
general purposes of, 245.
of herbivorous animals, 249.
liquid, absorption of, 281, 339.
of man, 249.
milk, a natural, 246.
mixed, the best for man, 253-56.
mixture of, necessary, 245-49.
nitrogenous and non-nitrogenous,
245.
oleaginous principles of, change
in stomach, 286
passage of through alimentary
canal, 256.
into stomach, 263.
relation of to carbonic acid pro-
duced, 214.
to excretion, 252-56.
to heat of body, 242.
to muscular action, 603.
of gastric fluid, 271.
of saliva, 260.
relation of to urea, 454.
to urine, 449.
phosphates in, 461.

800

Food, continued.
sulphur in, 460.
saccharine principles of, changes
in stomach, 286. _
solid, action of gastric fluid on, 281.
swallowing of, 273.
time occupied in passage of, 342.
vegetable, contains nitrogenous
principles, 249.
changes of in digestion, 280.
Foramen ovale, 767, 769.
Form of bodies, how estimated, 657.
Fornix, office of, 536.
Fourth ventricle, 511, 531.
cerebral nerve, 541.
Fovea centralis, 639, 641.
Freezing, effect of on blood, 67.
Frequency of heart’s action, 124. “
Functions of parts,
discharge of, attended with im-
pairment of tissue, 375.
growth from undue exercise of, 391.
Fundus of uterus, 716.
Fungiform papille of tongue, 700,
701.

G.

Galactophorous ducts, 784.
Gall-bladder, passage of bile into
and from, 326.
Ganglia, mode of action. See Ner-
vous Centres. ;
cerebral or sensory, functions of,

21.
of shal nerves, 493, 567.
of the sympathetic, 568.
structure of, 570.
action of, 573.
as co-ordinators of involuntary
movements, 573.
in heart, 131.
in substance of organs, 575.
Ganglion, Gasserian, 543, 568.
corpuscles, 473, 570. See-Nerve-
corpuscles.
Ganglionic fibres, 494.
Ganglionic nervous system. See
Sympathetic Nerves.
Gases, absorption of by blood, 371.
absorbed by the skin, 439.
in blood, 89.
in stomach and intestines, 343.
in urine, 463.

INDEX.

Gastric fluid, 271.
acid in, 275. A
action of on albuminous prin-

ciples, 284.
on food, 280-86.
favoured by division, 28o.
nature of, 279.
on saccharine and amylaccous
principles, 286.
artificial, 278.
characters of, 274.
composition of, 2b.
digestive power of, 276.
ayy with, 276-78, 281-
6.

pepsin in, 275.
quantity of, 272.
secretion of, 7b.
how excited, 273-74.
influence of nervous system on,

. 292.
Gastric veins, blood of, 87.

Gelatinous substances, 11.

Gelatin, digestion of, 284.
insufficient as food, 249.
properties of, 11.

Generation and development, 713.

Generative organs of the female,

714.
Genito-urinary tract of mucous.
membrane, 399.
Germinal area, 743.
matter, 20.
membrane, 742.
spot, 720. .
development of, 721
vesicle, 720.
development of, 721.
i earance of, 739.
Gizzard, toe of, 287.
Gland, pineal, 537.
pituitary, 538.
prostate, 731, 737.
Gland-cells, agents of secretion, 401.
relation to epithelium, 31, 401.
Gland-ducts, arrangement of, 404.
contractions of, 407.
Glands, aggregated, 403.
Brunn’s, 305.
ceruminous, 427.
conglomerate, 403.
Cowper’s, 731, 737:
ductless, 410.
Duverney’s, 718.

.
*»

-

ral

INDEX.

Glands, continued.
of large intestine, 310.
lenticular of intestine, 7.
of stomach, 270.
of Lieberkiihn, 299.
lymphatic. SeeLymphatic Glands.
of Peyer, 300.
mammary, 782.
salivary, 256.
sebaceous, 428.
secreting. See Secreting Glands.
of small intestine, 298.
of stomach, 268.
sudoriparous, 426.
tubular, 401.
of large intestine, 310.
of stomach, 268.
vascular, 410.
Glands.
vulvo-vaginal, 718.
Glandula Nabothi, 717.
Glandular epithelium, 31.
Glisson’s capsule, 315.
Globulin, 74.
Globus major and minor, 732.
Glosso-pharyngeal nerve, 553.
communications of, 554.
motor filaments in, 554.
@ nerve of common sensation and
of taste, 556, 704.
Glottis, action of leryngeal muscles
on, 609, 610.
closed in vomiting, 223, 289.
effect of division of pneumogastric
nerves on, 561.
forms assumed by, 610.
narrowing of, proportioned to
height of note, 612.
respiratory movements of, 200.
Glucose in blood, 83.
Gluten in vegetables, 249.
Glycocholic acid, 323.
Glycogen or glycogenic substance,

See Vascular

334.
Glucose, 7.
Graafian vesicles, 718.

formation and development of,

718, 723, 728.
constant, 723.

relation of ovum to, 718, 722.

rupture of, changes following, 727.
Granular layer of retina, 640.
Granules, 22. See Molecules.
Grape-sugar in blood, $3.

8oI

Grey matter of cerebellum, 525.

of cerebral ganglia, 521. .

of cerebrum, 532.

of crura cerebri, 518.

of medulla oblongata, 509.

of pons Varolii, 518.

of spinal cord, 490.

_ functions of, 496-498.
Groove, primitive, 743.

primitive dental, 54.
Growth, 390.

coincident with development, 2,

"ls am
compared with common nutrition,

393.

conditions of, 7.

continuance of, 391.

as hypertrophy, 392.

increased by increase of function,

391.

not peculiar to living beings, 2.
Gum, insufficient as food, 248.
Gustatory nerves, 555, 703.

H.

Habitual movements, 506.
Heematin, 77. \
Hemadynamometer, 152.
experiments on respiratory power
with, 204.
Hemodrometer, 155.
Hemoglobin, 74, 35, 219.
Hair, 428.
casting of, 378.
chemical composition of, 15.
development and growth of, 377.
growth near old ulcers, 393.
structure of, 428.
Hair follicles, 429.
their secretion, 432.
Halitus or odour of blood, 57.
Hamulus, 677.
Hand, principal seat of sense of
touch, 703.
Haversian canals, 48.
Hearing, anatomy of organs of, 671.
double, 695.
impaired. by lesion of facial nerve,
3
iaftabocs of external ear on, 688.
of labyrinth, 689-92.
of middle ear, 683-68¢.
3F

802

Hearing, continued.
physiology of, 679.
See Sound, Vibrations, ete.
Heart, 102-132.
action of, 109.
effects of, 132.
force of, 126. :
frequeney of, 124.
after removal, 129.
rhythmie, 128.
weakened in asphyxia, 228.
auricles of, 102.
their action, 109.
See Auricles.
chorde tendinez of, 106.
columne, carne of, 107.
course of blood in, 103.
development of, 763.
of cavities and septa, 765.
fleshy columns of, 107.
action of, III.
nglia of, 129.
: ypertrophy of, 392.
impulse of, 123.
uence of pheumogastric nerve,
131, 557; 559-
of sympathetic nerve, 129, 574,

575:
muscular fibres of, 587.
nervous connections with other
organs, 131.
sounds of, 119.
first, 120.
in relation to pulse, 160.
second, 121.
structure of, 102.
tendinous cords of, 106.
valves of, their action, 112.
arterial or semilunar, 108.
action of, 115.
auriculo-ventricular, 105.
action of, 114.
ventricles of, ‘their action, 110.
capacity, 128.
Hearts, lymphatic.
hearts.
Heat, action of on nerves, 476.
animal, 231. Sce Temperature.
adaptation to climate, 234.
connection of with respiration,
236-238.
influence of age on, 232.
of exercise, 232.
of external coverings, 243.

See Lymph-

INDEX.

Heat, continued.
of food, 242.
of nervous system, 243.
losses by radiation, etc., 238.
in relation to bile, 328.
_ sources and modes of produc-
tion, 236.
developed in contraction of mus-
cles, 233, 589.
perception of, 712.
Heat or rut, 724.
analogous to menstruation, 726.
Height, relation to respiratory capa-
city, 202.
Helicotrema, 677.
Helix of ear, 671.
Hemispheres, Cerebral. See Cere-
brum.
Hepatic cells, 316.
ducts, 314, 320.
veins, 319.
characters of blood in, 88.
vessels, arrangement of, 316.
Hepatin, 334.
Herbivorous animals,
perception of odours by, 634.
Hermaphroditism, apparent, 782.
Hiccough, mechanism of, 222.
Hilus of kidney, 440.
spleen, 412.
Hip-joint, pain in its diseases, 485,

499.
Hippuric acid in blood, 83.
in urine, 458.
we matter, chemist composition

: 15.
Horse’ s blood, ocala coagulation

of, 73:
cerebelium, 529.
Hunger, sensation of, 291.
Hyaline cartilage, 42
Hybernation, reba a, sapeene
etc., during, 231.
state of thymus in, 416.
temperature in, 238.
Hydrochloric acid in gastric fluid,

275,

Hydrophobia, spasms of, 488.

Hygrometric conditions "influencing
respiration, 214.

Hymen, 717.

Hypertrophy, 392.

Hypoglossal nerve, 565.

Hypospadias, 782.

I.
Ideas, connection of with cerebrum,

33:
Tleum, 297.

Tleo-ceecal valve, 297, 309.
structure and action, 311, 345.
Image, formation of on retina, 646.

distinctness of, 647.
inversion of, 652.
Impressions,
retained and. reproduced in cere-
brum, 533-
Impulse of heart, 122.
Ineus, 674.
function of, 686.
ean ead blood, coagulation of,
7.
corpuscles in, 73.
Infundibulum, 191.
Inhibitory influence of pneumo-
gastric nerve, 131.
Inhibitory nerves, 475.
Inorganic elements in human body,
17.
Insects, temperature of, 237.
Inspiration, 195. :
' elasticresistance overcome by, 206.
force employed in, 204.
during apnea, 206.
influence of on circulation, 174.
mechanism of, 195.
Instability of organic compounds, 9.
Intellectual faculties, relation to
cerebrum, 532.
Interarticular fibro-cartilage, 44.
Intercellular substance, 27.
Intercostal muscles, action in in-
spiration, 195.
in expiration, 199.
Interlobular veins, 317.
Intestinal canal, development of,
BO TIS bo
Intestines, digestion in, 297.
fatty discharges from, 313.
gases in, 343.
large, digestion in, 340.
glands of, 310.
structure of, 309.
movements of, 344.
small, changes of food in,.337.
glands of, 299.
structure of, 297.
valvule conniventes of, 298.

INDEX. | 803

Intestines, continued.
villi of, 306.
Intonation, 621.
Intralobular veins, 317.
Inversion of images on retina, 652.
correction of, 653.
Involuntary movements originated
by will, 523.
muscles, action of, 602.
structure of, 581.
Iris, 644.
action of, 540, 648.
in adaptation to distances, 651.
capillaries of, 159.
development of, 772.
influence of fifth nerve on, 546.
of sixth nerve, 541, note.
of third nerve, 540.
relation of to optic nerve, 540.
structure and function of, 644.
Iron 5 parts of body in which found,

18.
Irritability of muscular tissue, 587.
Iter a tertio ad quartum ventricu-
lum, 531. .
Ivory of teeth, 51.

’

J.

Jacob’s membrane, 640.

Jacobson’s nerve, 553.

Jejunum, 297.

Jetting flow of blood in arteries, 137.
Jumping, 601.

K.

Keratin, 15.
Kidney, increased function of one,

408.
Kidneys, their structure, 440.
blood-vessels of, how distributed,

443-
capillaries of, 159, 444.
development of, 777.
function of, 446. See Urine.
Malpighian bodies of, 443.
tubules of, 441.
Knee, pain of, in diseased hip, 485,

499.
E

Labia externa and interna, 717.
ce ie:

804.

Labyrinth of the ear, 675.
membranous, 678.
osseous, 676,
function of, 689.
Lacteals, 349.
absorption by, 363.
contain lymph in fasting, 358.
origin of, 350.
structure of, 353-
in villi, 308, 363.
Lactic acid in blood, 83.
in gastric fluid, 275.
Lactiferous ducts, 784.
Lacune of bone, 47, 48.
Lamelle of bone, 48.
Lamina spiralis, 677.
use of, 691.
Laminz dorsales, 743, 760.
viscerales or ventrales, 745, 761.
Language, how produced, 619.
Large intestine. See Intestine.
Laryngeal nerves, 557.
Larynx, construction of, 606.
influence of pneumogastric nerve
on, 558-561.
irritation referred to, 485.
muscles of, 609.
variations in according to sex and
- age, 615.
ventricles of, 619.
vocal cords of, 606, 609.
Laws of functions of nerves, 483.
Laxator tympani muscle, 674.
Lead an accidental element, 19.
Leaping, 601.
Legumen identical with casein, 249.
Lens, crystalline, 643.
Lenticular ganglion, relation of third
nerve to, 539.
Lenticular glands of stomach, 270.
of large intestine, 310.
Leucocytes, 76.
Leucocythemia, state of vascular
glands in, 417.
Levator palpebra superioris, nerve
supplying, 539.
Levers, different kinds of, 595.
Lieberkithn’s glands,
in large intestines, 310.
in stomach, 300,
Life,
animal, 464.
dependence of on medulla oblon-
gata, 513.

INDEX. . ie:

Life, continued. — |
is term, of, for each particle,

3:
organic, 464.
simplest manifestation of, 1.
Lightning, condition of blood after
death by, 68. .
Lime, salts of, in human body, 18.
phosphate of, in albumen, 13.
in blood, 81
in bones and teeth, 18, 45.
in tissues, 18.
Lingual branch of fifth nerve, 547,
_ 548, 555, 704.
Lips, influence of fifth nerve on
movements of, 545

Liquid part of food, absorption of,

281, 339.
Liquor amnii, 748.
Liquor sanguinis, 56, 60.
lymph derived from, 364.
still layer of in capillaries, 163.
Lithium, absorption of salts of, 371.
Liver, 314.
action of on albuminous matters,
332.
on saccharine matters, 7).
a blood-making organ, 102.
blood-vessels of, 318-21.
capillaries of, 159.
cells of, 316.
circulation in, 101,
development of, 775.
ducts of, 321.
functions of, 322.
in feetus, 328.
glycogenic function of, 333.
secretion of, 322. See Bile.
structure of, 314.
sugar formed by, 333-336.
test for presence of sugar in, 333
Living robe properties of, 1.
tissues, contact with, retards co-
agulation, 66.
Lobes of lungs, Igo.
Lobules of liver, 315.
of lungs, 190.
Locus niger, 520.
Love, physical, cerebellum, in rela-
tion to, 528.
Luminous circles produced by pres-
sure on eyeball, 665.
impressions, duration of, 659.

| Lungs, 187, 193.

INDEX,

Lungs, continued.
capillaries of, 159.
cells of, 191-193.
changes of air in, 208.
circulation in, 101, 209.
congestion of, in asphyxia, 229.
after division of pneumogastric
nerve, 562.
contraction of, 199.
coverings of, 188.
development of, 777.
elasticity of, 199.
intercellular passages in, I9I.
lobes of, 190.
lobules of, 190.
movements of in respiration, 194-
200.
nutrition of, 209.
position of, 187.
structure of, 187, 190.
supplied by pneumogastric nerve,
557) 559-
Lymph, analysis of, 360.
compared with chyle, 7.
with blood, 362.
general characters of, 357.
_ quantity formed, 362.
relation to blood, 361, 365.
Lymph-corpuscles, structure of, 358.
in blood, 92.
development ito blood-corpus-
cles, 93.
Lymph-hearts, structure and action
- of, x
relation. of to spinal cord, 366,

508.
Lymphatic glands, structure of,

354-
function of, 358.
Lymphatic vessels,
absorption by, 364.
communication with serous cavi-
ties, 352.
communication with
sels, 358.
contraction of, 354.
course of fluid in, 348.
<listribution of, 349.
origin of, 349.
propulsion of lymph by, 353.
structure of, 347, 353-
valves of, 353.
Lymphoid tissue.
Tissues.

blood-ves-

See Retiform

805

M.

Macula germinativa, 720.
Magnesium in human body, 18.
Maintenance or assimilation, nature
of the process. See Growth.
nutritive, 374.
of blood, 93.
Male sexual functions, 731.
voice, 614.
Malleus, 674.
function of, 686.
Malpighian bodies, 441, 443.
capsules, 442, 443, 444.
Mammary glands, 782.
ee an accidental element,
I

“Marginal fibro-cartilages, 44.

Marrow of bone, 45.
Mastication, 257.
fifth nerve supplies muscles of,

_544-
Mastoid cells, 673. .
Matrix of cartilage, 41.
of nails, 431.
Meatus of ear, 671.
urinarius, opening of in female,

717.
Mechanical irritation, violent, effect
on nerves, 476.

Meconium, biliary principlesin, 327.

Medulla of bone, 45.
of hair, 429.

Medulla oblongata, 509, 518.
analogy to spinal cord, 512.
columns of, 510.

distribution of fibres of, 511.
conduction of impressions in, 513.
congested in asphyxia, 228.
decussation of fibres in, 511, 512.
development of, 770.
effects of injury and disease of, 514.
fibres of, how distributed, 511.
functions of, 513.
important to maintenance of life,

2b.
influence on deglutition, 516.

on. respiration, 226, 514, 517.

on speech, 517. :
maintenance of power In, 517.
as a nerve centre, 513.
pyramids of, anterior, 511.

posterior, 512.
reflecting power of, 515.

806 .

Medulla, continued.
sensation and voluntary powernot
seated in, 517.
structure of, 509.
Medullary portion of kidney, 440.
substance of lymphatic glands,

ee of nerve-fibre, 466.

Membrana decidua, 754.
granulosa, 718.

development of into corpus lu-

teum, 730.

limitas, 640.
propria. See Basement membrane.
pupillaris, 772.
capsulo-pupillaris, 7.
tympani, 673. *
oe of, 684, 687.

Membrane, blastodermic, 742.
Jacob’s, 640.
ossification in, 49.
primary or basement.

ment membrane.
vitelline, 719, 740.

Membranes, mucous.

membranes.

Membranes, serous. See

membranes.

Membranes, passage

through, 368.
secreting, 395.
Membranous labyrinth, 676, 678.
Memory, relation to cerebral hemi-
spheres, 533.

Menstruation, 724.
analogous with heat, 726.
coincident with discharge of ova,

725,
corpus luteum of, 730.
phenomena of, 727.
time of appearance and cessation,
726.
Menstrual discharge, composition
of, 727.

Mental derangement, 535- |

exertion, effect on heat of body,
243.
on phosphates in urme,. 461.

See Base-

See Mucous
Serous

of fluids

faculties, development of in pro- |

portion to brain, 533.
theory of special localisation of,
534-530.
field of vision, 654.
Mercury, absorption of, 372, 438.

INDEX.

Mesenteric arteries, contraction of,

140.
veins, blood of, 87.
Meshes of capillary network, 159.
Mesocephalon, 518.
Metallic substances, absorption of
by skin, 437.
Mezzo-soprano voice, 615.
Micturition, action of spinal cord
in, 505.
Milk, as food, 246.
properties of, 785.
secretion of, 784.
Milk-globules, 785.
Milk-teeth, 55.
Mind, cerebral hemisphere the
organs of, 533-536. .
iniluence on action of heart, 128.
on animal heat, 243.
on digestion, 283, 294.
on hearing, 693.
on movements ofintestines, 346.
on nutrition, 383.
on respiratory acts, 226, 294.
on secretion, 408.
on secretion of saliva, 260.
in taste, 704.
in touch, 707.
in vision, 653-660.
perception of special sensations
Yy, 623. .
independently of organs, 625.
perception of transferred impres-
sions, 486. ;
power of concentration on the
senses, 658.
of exciting sensations, 712.
reflex movements independent of,
500. °
sensitive impressions referred to
parts by, 481.
Mitral valve, 105.
Mixed food for man, 252.
necessity of, 246.
Modiolus, 676.
Molecules, or granules, 22.
in blood, 78. :
in milk, 785.
movement of in cells, 27.
Molecular base of chyle, 358.
motion, 23.
Monotonous voice, 614.
Mortification from deficient blood,

384.

INDEX,

weney, causes and phenomena of,
579.
. ciliary, 578. See Cilia.
molecular, 23.
muscular, 580. .
action on bones as levers, 595.
nerves of, 476.
of objects, how judged, 657.
power of, not essentially distinc-
tive of animals, 5.
sensation of, 627.
Motor impulses, transmission of in
cord, 499.
nerve-fibres, 475.
nerves, cranial, 539.
' laws of action of, 482.
roots of spinal nerves, 493, 565.
Motor lingue nerve, 565.
oculi, or third nerve, 539.
Motorial end-plates, 471.
Mouth, changes of food in, 256.
moistened with saliva, 260.
Movements of intestines, 344.
of muscles, 595.
habitual, 506, 523.
reflex. Sce Reflex Actions.
sensation of, 710.
symmetrical, 542.
produced by irritation of auditory
nerve, 697. .
of respiration, 200,
of stomach, 287.
Mucous layer of blastodermic mem-
brane, 742.
Mucous membranes, 398.
basement membrane of, 399, 400.
capillaries of, 159. — -
component structures of, 399.
epithelium-cells of, 400.
Epithelium.
gland-cells of, 400.
tracts of, 398.
of intestines, 298, 310.
of stomach, 266.
of tongue, 698.
of uterus, changes of in preg-
nancy, 752.
Mucus, nature of, 15.
acid, of vagina, 57.
in bile, 322.
of mouth, mixed with saliva, 258.
in urine, 459.
Multipolar nerve-cells, 474.
Muscles of animal life, 583.

See

807

Muscles, continued.
assisting erection, 185.
assisting vomiting, 289. |
changes in, by exercise, 375.
contraction of, 588.
effect of pressure of, on veins, 170.
heat i di in contraction of,
599.
‘Involuntary, 581.
moving eyeball, 539.
larynx, 609.
nerves of, 587.
nutrition of, 385.
of organic life, 583.
sensibility of, 588.
sound developed in contraction
of, 591.
source of action of, 602.
striated, 583, 588.
voluntary, 583.
action of, 595.
blood-vessels and nerves of,
586, 587.
work of, how estimated, 603.
Muscular coat of arteries, 133, 138.
of large intestine, 309. —
of small intestine, 297, 298.
of stomach, 265.
fibres, involuntary, 581.
voluntary, 584.
of stomach, action of, 287.
of villi in intestines, 307.
force, idea of, how derived, 710.
motion, 580.
movements. See Movements.
sense, 587, 709.
cerebellum the organ of, 528.
strength tested by respiratory
efforts, 204.
tissue, of animal life, 583.
in arteries, 133.
contractility of, 587.
contraction of, 588.
heat developed in, 589.
sound in, 590.
effect of stimuli on, 476, 590.
of heart, 586.
involuntary, 581.
irritability of, 587.
duration of, after death, 592.
of organic life, 583.
Lelie of, 587.
rigidity of, after death, 592.
sensibility of, 588.

808

Muscular, continued.
striped, 583.
structure of, 583-586.
unstriped, 580-583.
situations where found, 582.
structure of, 70.
in veins, 167.
tone, 508.
Muscularis Mucose, 267, 298, 306,
307.
Muscularity,
of arteries, 138. ;
evidence of, 140.
urposes of, I4I.
of y saplation 353-
of lymph-hearts, 366.
Musical sounds, 614.
Myopia, or short-sightedness, 651.
Myosin, 15.
a.

Nabothi glandule, 717.

Nails,
chemical composition of, 15.
structure of, 431.
growth of, 7.

Narcotic poisons in stomach, ex-

periments on, 293.
Nasal cavities in relation to smell,
633-

Nates (brain), 520.

Natural organic compounds, 9.
classification of, 10.

Nerve, depressor, "563.

Nerve-centres, 465. See Cerebel-

lum, cerebrum, etc.

_ conduction in or through, 484.
congestion of in asphyxia, 230.
diffusion or radiation in, 486.
functions of, 483.
perception in, 484.
reflexion in, 486.

conditions of, 487.
transference of impressionsin, 485.
vaso-motor, 576.

Nerve-corpuscles, 473.
caudate or stellate, 474.
of retina, 641.
simple, 474.

Nerve-fibres, 465-483.
axis-cylinder of, 466.
cerebro-spinal, 465.
conduction of impressions by, 477.

of one kind only, 478.

INDEX.

Nerve-fibres, continued.
rate of, 478.
continuity of, 470.
“course of, 470.
difference in function notattended
by difference of structure, 475.
effects of injury and cha 479;
480, 482.
fasciculi of, 470.
force not generated by, 475-
functions of, 474.
effect of chemical stimulation,

ATT. oie
of mechanical irritation, 476,

479.
of temperature, 476.
impressions on, referred to peri-
phery, 481.
kinds of, 465.
laws of action, 477.
of motor nerves, 482.
of sensitive nerves, 478.
medullary or white substance of,
466.
plexuses of; 470,
of retina, 641.
size of, 467.
structure of, 465.
sympathetic, 468.”
terminations of, 470.
in cells, 471.
in free ends, ¢.
in motorial end-plates, 2b.
in networks or plexuses, 7).
in special terminal organs, 7.
Nerves,
action of stimuli on, 47 S477.
afferent, 475.
centrifugal,47 5.
centripetal, 2.
cerebral, physiology of, 5 38. See
Cerebral Nerves.
efferent, 475.
excito-vaso-motor, 577-
inhibitory, 131, 475.
of motion, or motor, \475.
laws of action in, 482.
respiratory, 226.
of sensation, or sensitive, 475.
. laws of action in, 478.
of special sense, 538.
secretory, 409, 475.
spinal, 493. See Spinal Nerves.
stimuli of, 476.

INDEX. re 809

Nerves, continued.
structure of, 465.
sympathetic. See Sympathetic
Nerve.
trophic, 388, 475.
ulnar, effect of compressionof, 479.
of division of, 482.
vaso-inhibitory, 577.
vaso-motor, 142, 576.
Nervi-nervorum, 481.
Nervous force, velocity of, 488.
layer of retina, 641.

_ Nervous substance, changes in from

mental exertion, 376.
fibrous, 465.
phosphorus in urine from, 461.
vesicular, 464, 473.

Nervous system, 463.
cerebro-spinal, 463, 488.
development of, 743, 770.
elementary structure of, 464. See

Nerve-corpuscles, and Nerve-
fibres.
infiuence of, on animal heat, 243.
on arteries, 142.
on contractility, 587.
on contraction of blood-vessels,
142, 577-
on erection, 184.
on gastric digestion, 291.
on the heart's action, 129.
onmovements of intestines, 346.
of stomach, 294.
on nutrition, 385.
on respiration, 226.
on secretion, 408.
on sphincter ani, 346.
of organic life, 464, 568.
sympathetic, 464.
Nervous abducens seu ocularis ex-
ternus, 541.
patheticus seu trochlearis, 541.
vagus, 557. See Pneumogastric.

Networks, capillary, 157. See Capil-

laries.

Neuralgia, division ofnerves for, 480.

New-born animals, heat of, 232.

Ninth cerebral nerve, 565.

Nipple, an erectile organ, 183.
structure of, 784.

Nitrogen in blood, 89, 90.
influence of in decomposition, 10.
in relation to food, 253.
in respiration, 216.

Nitrogenous food, 245, 248.
in relation to muscular work,
603.
in relation to urea, 454.
to uric acid, 456.
principles, 11.
Noise, how produced, 692.
Noises in ears, 696.
Nose. See Smell.
irritation referred to, 486.
restoration of, sensitive pheno-
mena in, 481.
Non-azotised or Non-nitrogenous
food, 245.
organic principles, Io.
se oe parts, nutrition of,

385.
Nuclei,
description of, 23.
in sae eae and growing parts,
382.
Nucleoli or nucleus-corpuscles, 23.
Nutrition compared with secretion,
405. P
conditions necessary to, 383.
examples of, 376.
general nature of, 374.
influence of conditions of ,blood
on, 383.
of nervous system on, 385, 548.
of state of part on, 389.
of supply of blood on, 384.
of sympathetic nerves on, 575.
in paralysed parts, 386.
in vascular and non-vascular
parts, 385.
Nutritive,
repetition, 382.
reproduction, 70.
Nymphe, 717.

0.

Oblique muscles of the eye, action
of, 543-
Ocular cleft, 773.
spectrum, 659.
dours,
causes of, 630.
different kinds of, 634.
- perception of, 630.
varies in different classes, 634.
relation to taste, 705.

SIO

(Esophagus, action of in deglutition,
265.
reflex movements of, 500.
Oil, absorption of, 364, 373.
Oily matter, 11.
coated with albumen, 359.
Oleaginous principles, digestion of,
286, 313, 330, 338.
Olein, II.
Olfactory cells, 632.
lobes, functions of, 521.
nerve, 631.
subjective sensations of, 635.
Olivary body, 511.
fasciculus, 512.
Ophthalmic ganglion, relation of
thirdnerve to, 539.
Optic lobes, corpora quadrigemina,
homologues of, 521.
functions of, 521.
nerve, decussation of, 668.
fibres of, 475."
point of entrance insensible to
sight, 663.
thalamus, function of, 521.
vesicle, primary, 770.
secondary, 772.
Optical angle, 655.
Ora serrata of retina, 638.
Oral canal and oral opening, 620.
Organie compounds, instability of,9.
peculiarities of some, 8.
processes, influence of sympathetic
nerve upon, 573.
Organisation, definition of, 8.
Organs, plurality of cer ebral, 534.
Organs of sense, dey elopment of, 770.
Os orbiculare, 674.
Os uteri, 717. ,
Osmosis, 368.
Osseous labyrinth, 676.
Ossicles of the ear, 674.
office of, 685.
Ossicula auditus, 674.
Ossification, 49.
Otoconia or Otolithes, 679.
use of, 690.
Ovaries, 714.
enlargement of at puberty, 723.
Graafian vesicles in, 718.
Ovisacs, 718.
Ovula Nabothi, 717.
Ovum, 719.
action of seminal fluid on, 738.

INDEX. —

Ovum, continued.
changes of in ovary, 722.
previous to formation of em-
bryo, 739.
subsequent to cleaving, 741. .
in uterus, 742.
cleaving of yelk, 740.
connection of with uterus, 751.
discharge of from ovary, 72 3:
formation of, 721.
germinal membrane of, 742..
germinal vesicle and spot of, 720.
. Impregnation of, 731.
structure of, 719.
Oviduct, or Fallopian. tube, 714, 715.
Oxalic acid in urine, 463.
Oxygen,
in blood, 89, 219.
consumed in breathin , 210, 215.
effects of, on colour of “blood, 85.
on pulmonary circulation, 160.
proportion of to carbonic acid,
215.
union with carbon and hydrogen,
producing heat, 236.

zs

Pacinian bodies or corpuscles, 471.
Pain excited by the mind, 712.
in paralysed parts, 479.
Palate in relation to deglutition, 264.
nerves of, 559.
Palate and uvulai in see i to voice,
618.
Palmitin, 11. 3
Pancreas, 312. ;
development of, 775.
functions of, 312.
Pancreatic fluid, 312.
Pancreatin, 7b.
Papille,
of the kidney, 441.
of skin, distribution of, 421.
end-bulbs in, 425, 426.
epithelium of, 425.
nerve-fibres in, 422.
supply of blood to, 422.
touch corpuscles in, 423.
of teeth, 54. ee
of tongue, 698, 700.
circumvallate or calyciform,
701.

INDEX.

Papille, continued.
of tongue, conical or filiform, 7or.
fungiform, 7d.
use of, 703.
Paraglobulin, 74.
Par vagum. See Pneumogastric
nerve.
Paralysed parts,
pain in, 479.
nutrition of, 386.
limbs, temperature of, 243.
preservation of sensibility in, 481.
Paralysis, cross, 513.
seat of, according to part of cere-
bro-spinal axis injured, 496.
Paraplegia,
delivery in, 506.
influence of spinal cord shown in,

reflex movements in, 501.
state of intestines in, 346.
Parotid gland, saliva from, 259.
Particles,
changes of in nutrition, 375.
duration of life in each, 381.
natural decay and death, 376.
process of forming new, 382. _
removal when impaired or effete,
376.
Parturition, mechanism of, 224.
Patheticus, or fourth nerve, 541.
Pause in heart’s action, 119, 120.
respiratory, 200.
Peduncles,
of the cerebellum, 525.
of the cerebrum, 531.
Pelvis of the kidney, 441.
Penis,
corpus cavernosum of, 183.
development of, 782.
erection of, explained, 183.
reflex action in, 184, 505.
Pepsin, 16, 275.
Peptone, 285.
Perception of sensations by cerebral
hemispheres, 484, 532.
Perichondrium, 42.
Perilymph, or fluid of labyrinth of
ear, 678.
use of, 689.
Periosteum, 42.
Peristaltic movements of intestines,

344-
of stomach, 288.

SIE

Permanent cartilage, 41.

teeth, 50.

Perspiration, cutaneous, 432.
insensible and sensible, 434.
ordinary constituents of, <b.

Peyer’s glands, 301%.
functions of, 303.
patches, 301.
resemblance to vascular glands,

305; 410.
structure of, 302.

Pharynx,

action of in swallowing, 264, 500,
60.
influence of glosso-pharyngeal
nerve on, 544.
of pneumogastric
558, 559.

Phosphates in tissues, 17.

present in albumen, 13.
in blood, 80, 82.
in urine, 462.
Phosphorus in human body, .17.
union of with oxygen producing
heat, 236, note.
in urine, source of, 462.
Phrenology, 535.

nerve on,

Physiology, definition of, 1.

Pia mater, circulation in, 181.
Pigment, 39. .
of choroid coat of eye, 637.
composition of, 41.
of hair, 378, 429.
of skin, 420.
uses of, 41.
Pigment cells, form of, 26, 40.
Pineal gland, 537.
Pinna of ear, 671.
‘Pins and needles,” sensation of,

479.
Pitch of voice, 618.
Pith of hair, 429.
Pituitary gland, 537.
Placenta, 749, 752.
formation of, 755.
foetal and maternal, 757.
relation of to the liver, 328.
structures composing, 757.
Plants,
distinctions from animals, 4.
Plexuses of nerves, 470.
terminal, 471.
of spinal nerves, relation to cord,

492.

812 , ‘

Pneumogastric nerve, 557.
distribution of, 557.
mixed function of, 558.
influence on action of heart, 131.
on deglutition, 265.
on digestion, 293.
on functions of larynx, 558,

559-
of esophagus, 559.
of lungs, 7
of pharynx, 558, 559.
on movements of stomach,
204.
on respiration, 514, 561.
on secretion of gastric fluid,
293, 294.
on sensation of hunger, 291.
of thirst, 292.
origin of from medulla oblongata,
514.
Poisoned wounds, absorption from,

373-
Poisons, narcotic, introduced in
stomach, 293. ;
Polarity of muscles, 595, note.
Polygamous birds, their cerebella,

529.
Pons Varolii, its structure, 518.
Portal blood, characters of, 87.
canals, 316.
circulation, 102.
function of spleen with regard
to, 418.
veins, arrangement of, 316.
Portio dura, of seventh nerve, 550.
mollis, of seventh nerve, 679.
Post mortem rigidity. See Rigor
Mortis.
Posture, effect of on the heart’s
action, 125.
Potassium, salts of, in fluids and
tissues, 17.
Pregnancy, absence of menstruation
during, 727.
corpus luteum of, 731.
influence on blood, 83.
: a ig or long-sightedness,
2

Pressure on eye, effects of, 665.
Primary membrane, 395, 400.
Primitive, dental groove, 54,

fasciculi and fibrils of muscle,

583,-585.
groove in embryo, 743.

INDEX.

Principles, nitrogenous, II.
non-nitrogenous, IO. :
Process, vermiform, 524.
Processus ilis, 674.
a cerebello ad testes, 531.
Prostate gland, 731.
functions of secretion unknown,
737-

Protagon, 74.

Proteids, 245.

Protein-compounids, 12.

Protoplasm, 20, 77.

Ptyalin, action of, 262.

Puberty,
changes at period of, 723. _
indicated by menstruation, 726.

Pudenda, 717.

Pulmonary artery, valvesof, 108, 119.
capillaries, 192.
circulation, IOI.

influence of carbonic acid on,
228.
of pneumogastric nerve on,
561. : a
velocity of, 179.

Pulp of hair, 378.
of teeth, 51.

Pulse, arterial, 143.

* eause of, 2b.
dicrotous, I51.
difference of time in, 145.
explanation of, 148.

frequency of, 124.
influence of age in, 7. |
of food, posture, etc., 125. . iZ
observations on with sphygmo- ~~
graph, 146-148. ,
relation of to respiration, 126.
tracings of, 148, 151.
in large arteries, 150.
in radial artery, 151.
variations in, 124-126.
in capillaries, 160, 161. x

Pupil of eye, office of, 644. ~¥
relation of third nerve to, 540. }

Purgative action of bile, 327.

Pus, contains albumen, 13.
Putrefaction. See Decomposition.
arrested by gastric fluid, 274.

Pylorus, structure of, 266.
action of, 287, 288. \ _

Pyramidal portion of kidney, 440. =.

Pyramids of medulla oblongata, ;

511, 512.

INDEX

Q.
Quadrupeds, retin of, 667.

R.

Radiation of impressions, 486, 499.
Rectum, 309.
evacuation of, a reflex act, 505.
mechanism of, 292.
Reflexion of impressions, 486.
by medulla oblongata, 515.
by spinal cord, ps
Reflex actions, 486, 499.
in accidents, 506.
conditions necessary to, 487.
in disease, 507.
examples of, 501, 505.
excito-motor and sensori-motor,
504, note.
general rules of, 487.
independent of mind, 487, 501-505.
influence of cord on, 500, 507.
irregular in disease, 487.
after separation of cord from
brain, 501, 505.
purposive in health, 487.
relation of fifth nerve to, 546.
relation to volition, 505.
to walking,1rnning, ete., 506.
sustained, 488.
in tetanus, etc., 507.
Reflex functions of medulla oblon-
gata, 515.
of spinal cord, 500.
Refracting miedia of eye, 642.
Refraction, laws of, 642.
Renal arteries, arrangement of, 444.
veins, blood of, 89.
Repair. See Nutrition.
retarded in paralysed parts, 386.
Repetition, nutritive, 382.
Reproduction, nutritive, 7d.
Reserve air, 201.
Residual air, 2.
Respiration, 186.
abdominal type of, 198.
ammonia and other products ex-
haled by, 218.
carbonic acid increased by, 211.
changes of air in, 210. |
of blood in, 219.
costal types of, 198.

813
Respiration, continued.
force of, 203-207.
frequency of, 203.
influence of brain on, 504.
of medulla oblongata, 225-227,
513-516.
of pneumogastric nerve, 514, 560.
mechanism of, 194.
movements of, 195. See Respira-
tory movements.
of air in, 208.
of blood in, 7.
nitrogen in relation to, 216.
oxygen diminished by, 215.
quantity of air changed in, 201.
relation of to the pulse, 126.
structure of organs of, 188-194.
suspension and arrest of, 227.
temperature of air increased by,
210.
types of, 198.
watery vapour exhaled in, 217.
Respiratory capacity of chest, 202.
function of skin, 436.
movements, 195-199.
of air tubes, 207.
centre of, the medulla oblongata,
514.
effect of on circulation, 173.
excited through nerves, 515.
by various stimuli, 516.
of expiration, 198.
of glottis, 200.
influence on amount of carbonic
acid, 212.
of inspiration, 195.
relation to will, 504.
various, mechanism of, 200.
muscles, 195, 199.
power of, 204.
secondary, 227.
nerves, 227.
thythm, 200.
tract of mucous membrane, 399.
Rest, favourable to coagulation, 66.
Restiform bodies, 510, 512.
Retching, explanation of, 290.
Rete mucosum, 420.
testis, 732.
Retiform tissue, 267, 298, 355.
Retina, 638. ©
duration of impressions on, 659.
of after-sensations, 659.
effect of pressure on, 665.

or

814 _ INDEX,

Retina, continued.
focal distance of, 649.
function of, 641.
image on, how formed distinctly,
- 647.
ieee of, how corrected, 653.
insensible at entrance of optic
nerve, 663.
insufficient alone for distinct
vision, 642.
in quadrupeds, 667.
reciprocal action of parts of, 661.
in relation to direction of vision,
656.
to st Bn of bodies, 657.
to single vision, 664.
to size of field of vision, 654.
structure of, 638.
Rhythm of heart, cause of, 128.
See Heart.
respiratory, 200.
Rigor mortis, 592.
affects all classes of muscles, 594.
phenomena and causes of, 593.

Rima glottidis, movements of in re-

spiration, 200.
Rods of Corti, 678.
use of, 692.
Root of nail, 431.
Root-sheath of hair, 431.
Roots of spinal nerves, 490, 493.
anterior and posterior, special pro-
perties of, 494.
Rotation,
following injury of crura cerebelli,

530.
produced by dividing the crura
cerebri, 521
Rouleaux, formation ofin blood, 62,

73-
Rubbing, influence on cutaneous ab-
sorption, 437. ;
Rugee or folds of stomach, 266.
Rumination, 290.
Running, mechanism of, 602.
Rut or heat, 724.

S.

Saccharine principles of food, diges-
tion of, 286.
action of bile on, 332.
absorption of, 339.

Sacculus, 678.
Safety-valve action of tricuspid
valve, I15.
Saline constituents of bile, 324.
Saline constituents of blood, 82.
use of, 97.
of urine, 460.
matters, absorption of, 369.
Saliva, action of on food, 262.
on starch, 263.
composition of, 260,
digestive properties of, 262.
mechanical purposes of, 261.
organs for production of, 258.
physical properties of, 259.
purposes of, 261.
quantity secreted, 260.
rate of secretion, ib.
reaction of, 259.
relation to gastric fluid, 263.
Salivary Be 256.
development of, 774.
Salts, alkaline and earthy, influence
on coagulation, 65. .
Sarcode, 20.
Sarcolemma, 584.
Sarcous elements, 585.
Scala media, 677,
tympani, 677.
vestibuli, 7b.
Sclerotic, 637, 645.
Scurvy from want of vegetables, 255.
Season, influence on carbonic acid
expired, 213.
Sebaceous glands, 428.
their secretion, 432.
Secreting glands, 4or.
aggregated, 403.
convoluted tubular, 403.
tubular or simple, 4o1.
Secreting membranes. See Mucous
and serous membranes.
Secretion, 394. ;
action of cells and nuclei in, 404.
apparatus necessary for, 395.
circumstances influencing, 407.
discharge of, 406.
general nature of, 394.
influence of nervous system on,

408.
of sympathetic nerve, 573.
of quantity of blood, 407. —
process of, 394.
relation or antagonism of, 409.

INDEX.

Secretion, continued.
resemblance to nutrition, 405.
by membranes, 395.

mucous, 398.
serous, 395.
synovial, 398.
in vascular glands, 408. .
Selection of materials for absorption,
363.

Semicireular canals of ear, 676.
development of, 773.
use of, 689.

_ Similunar valves, 108.
action of, I15.

Seminal fluid, 734.

composition of, 738.
corpuscles and granules of, 734.
emission of, a reflex act, 505.
influence on ovum and embryo,
738.

filaments, 734.
purpose of, 735.

tubes, 732.

vesicles, 735.

Sensation attended by ideas, 711,
cerebral nerves of, 538. —’
common, 623.
conditions necessary to, 711.
conduction of in spinal cord, 496.
contrasts in, 712.
definition of, 623
excited by mind, 712.

by internal causes, 626.
of hunger, 291.
influence of attention on, 629, 658.
influence of mind necessary to, 711.
of motion, how perceived, 627.
muscular, 588, 709-711.
of necessity of breathing, 292.
nerves of, 475.
convey impressions to centres
only, 478.
impressions on referred to peri-
phery, 479-481.
laws of action of, 488.
perceived in cerebrum, 532.
preservation of in paralysed
nerves, 482.
referred to exterior, 482.
special, 623.
stimuli of, 475-477.
of special, 624-626.
in stumps, 481.
subjective, 712.

815

Sensation, continued.
of thirst, 291.
sympathetic, 487.
touch a modification of, 706.
transference and radiation of,
487, 499.
two kinds of, 623.
of volatile bodies, 628.
of weight, 710.
Sense,
of hearing, 671.
Sound.
of sight, 636. See Vision.
of smell, 7. See Smell.
of taste, 697. See Taste.
of touch. See Touch.
muscular, 528, 709-711.
special, nerves of, 538.
organs of, development of, 770.
Senses, special, general properties
of, 623.
action of external and internal
stimuli on, 625.
impairment, of from division of
the facial nerve, 551.
from division of the fifth nerve,

See Hearing,

547-
influence of attention on, 629.
ofinternalimpressions onnerves
of, 626.
qualities of external matter per-
ceived by, 623, 627.
special nerves of, 623.
stimulus excites in each nerve its
own sensation, 624.
Sensitive impressions, conduction of,

479.
by spinal cord, 496, 498.
reference of, 480-482.
nerves, 476.
Sensory ganglia, 523.
Septum between auricles, formation
of, 767.
between ventricles, formation of,

767.

Serosity of blood, 79.

Serous layer of blastodermic mem-
brane, 742, 745.

Serous membranes, 395.
arrangement of, 396.
communication of lymphatics

with, 352.
epithelium of, 395.
fluid secreted by, 397.

816 INDEX, ve an

Serous membranes, continued.

lining joints, etc., 396.
visceral cavities, 7b.

purpose of, 396.
stomata, 353.
structure of, 395.

Serum,
of blood, 78.
chief source of albumen, 13.
separation of, 60, 78.

Seventh cerebral nerve, auditory

em 679, 692.
facial portion, 550.
Sex, influence on blood, 83.

inflflence on production of car-

bonic acid, 211.

relation of to capacity of chest, 203.
to respiratory movements, 198.
Sexual organs and functions in the

female, 714-731.
in the male, 731-739.

Sexual passion, connection of with

cerebellum, 528.
Sighing, mechanism of, 221.
Sight. Sce Vision.

Silica, parts in which found, 17.
Singing, mechanism of, 614.
Single vision, conditions of, 664.
Sinus terminalis, 750.
urogenitalis, 779.
Sinuses of dura mater, 181.
Sixth cerebral nerve, 541. -
Size of field of vision, 654-657.
Skin, 419.
absorption by, 437.
of gases, 439.
of metallic substances, 437.
of water, 7d,
capillaries of, 161.
cutis vera of, 421.
epidermis of, 419.
evaporation from, 439.
excretion by, 432-437.

exhalation of carbonic acid from,

436.

of watery vapour from, 434.
functions of, 419.

respiratory, 436.
papille of, 423-426.
perspiration of, 433.
rete mucosum of, 420.
sebaceous glands of, 428.
structure of, 419.
sudoriparous glands of, 426.

Sleep, influence of on production of
carbonic aeid, 215.
Smell, sense of, 630. : ;
conditions of, 630.
different kinds of odours, 634.
impaired by lesion of facial nerve,

551.
impaired by lesion of fifth neki ae

547-
internal excitants of, 635.
limited to olfactory region, 633.
relation to common sensibility,
633.
structure of organ of, 631.
_ subjective sensations of, 635.
varies in different animals, 634.

; Snvering, caused by sun’s light, 486.

mechanism of, 223.
Sniffing, mechanism of, 224. .
smell aided by, 631-3
Soda, salts of in blood, 80.
in solids and fluids, 17.
Sodium in human body, 17.
chloride of, in albumen, 13.
Solid food, action of gastric fluid on,

276.
Solitary tie 301.

Sonorous vibrations, how communi-

cated in ear, ‘683, 03%;
in air and water, 683. Sce Sound.
Soprano voice, 614.
Sound,
conduction of by ear, 679.
by external ear, 680-682.
by internal ear, 689-692.
by middle ear, 683-689.
movements and sensations pro-
duced by, 697. -
perception of, 692.
of direction of, 693.
of distance of, 694.
a state of the auditory nerve,
695. ,
permanence of sensation of, 694.
produced by contraction of mus-
cle, 590.
production of, 692.
subjective, 696.
Sounds as expressions of passion, —

14.
classified, 614.
of heart, 1109.
causes of, 120.
Sources of nervous force, 484.

INDEX.

Spasms, reflex acts, 507.
Speaking, 614.

mechanism of, 224.
Special sense. See Senses.
Spectrum-analysis, 86.

of blood, 86.
Spectrum, ocular, 659-61.
Speech, 619.

function of tongue in, 622.

influence of medulla oblongata

on, 517.

Spermatozoids, development of, 734,

form and structure of, 7.
function of, 735.
motion of, 734.
Spherical aberration, how corrected
in the eye, 648.
Spheroidal epithelium, 30.
Sphincter ani,
external, 345.
internal, 310, 345.
influence of spinal cord on, 501,
508.
Sphygmograph, 146.
Spinal accessory nerve, 564. See
Accessory nerve.
Spinal cord, 488.
canal of, 490.
a collection of nervous centres,
508.
columns of, 494.
commissure of, 7.
conduction of impressions by,
495-499.
course of fibres in, 491.
decussation of sensitive im-
pressions in, 499.
effect of injuries of, on conduc-
tion of impressions, 496.
on nutrition, 386-88.
enlargement of parts of, 493.
fissures and furrows of, 490.
functions of, 496-509.
of columns, 496.

influence of on heart’saction, 128-

on lymph-hearts, 366, 508.
on sphincter ani, 500, 508.
on tone, 509.

morbid irritability of, 507.

nerves of, 493-95.

reflex function of, 500. See Re-
flex action.

size of parts of, 492.

» structure of, 490.

817

Spinal, cord, continued.
transference and radiation in,
_ . 485, 499.
Spinal nerves,
origin of, 493.
physiology of, 564.
Spiral canal of cochlea, 676.
lamina of cochlea, 677.
function of, 691.
Spleen,
as a blood-forming organ, 417.
in relation to digestion, 418.
to portal circulation, 7b.
hilus of, 412.
Malpighian corpuscles of, 413.
pulp, 412.
structure of, 411.
trabecule of, 411.
stroma of, 412.
Splenic vein, blood of, 87.
Spontaneous decomposition, 9.
Spot, germinal, 720.
Squamous epithelium, 30.
Stapedius muscle, 674.
function of, 688.
Stapes, 674, 676.
Starch,
action of cooking on, 286.
of pancreatic secretion, 313.
of saliva, 262.
of various substances, 720.
animal, 334.
digestion of in small intestine,

aa
in stomach, 286.
Starvation, 250.
loss of weight in, 250. |
effect on temperature, 251.
symptoms, 251.
period of death in, 252.
appearance after death, 252.
Statical pressure of blood, 152.
Stature, relation to capacity of
chest, 202.
Stearin, 10.
Stellate nerve-corpuscles, 474.
Stercorin, 342.
allied to cholesterin, 323.
Stereoscope, 671.
Still layer in capillaries, 163.
Stimuli, as excitants of contrac-
tility, 590-92.
of sensation, 476, 478.
of special senses, 624-26.
3 OG

Sulphur, continued.
in urine, 461.

818 INDEX.
St. Martin, Alexis, case of, 272,

277, 281.
Stomach,

plood-vessels of, 271.
development of, 774.
digestion in, 280-86.

influence of nervous system

on, 291.
digestion of after death, 294.
examined through fistul, 272,
281.
glands of, 268.
lenticular, 270.
tubular, 268.
movements of, 287. \
influence of nervous system
on, 294.
in vomiting, 289.
mucous membrane of, 266.
muscular coat of, 265.
passage of substances from to
urine, 446.
presence of not absolutely dis-
tinctive of animals, 7.
in relation to hunger, 291.
secretion of, 271. See Gastric
fluid.
structure of, 265.
temperature of, 272. \
Striped muscular fibre, 583-87.
Stroma of ovary, 715.
Structural changes of food in sto-
mach, 283.
Structural composition of hema
body, 19.
Stumps, sensations in, 481.
Subjeetive sensations, 712.
of sound, 696.
of taste, 706.
Sublobular veins, 318.
Sucking, mechanism of, 225.
Sudoriparous glands, 426.
their distribution, 427.
number of, 7b.
their secretion, 433-
Suffocation, 228-31.
Sugar, digestion of, 286, 332.
as food, experiments ‘With, 248.
formation of in liver, 333-40.
Sulphates in urine, 460.
Sulphur, in bile, 325.
in human body, 17.
union of with oxygen producing
heat, 216, 236, note.

Suprarenal capsules, 410, 411.
evelopment of, 777.
disease of, relation to discolora-
tion of skin, 416, note.
Swallowing, 263.
Sweat, 432.
Sympathetic nerve, 567.
character of movements exe-
cuted through, 575.
communication of with fifth
nerve, 549, 568.

with glosso-pharyngeal nerve, -

568.
with pneumogastric Si aehi
558, 568.
with sixth nerve, 541.
with spinal nerves, 568.
conduction of impressions by,
572.
divisions of, 567.
fibres of, course of, 570.
differences of from cerebro-
spinal fibres, 468, 568.
mixture with cerebro-spinal
fibres, 571.
relation to print ai. sys-
tem, 577.
ganglia of, 567.
action of, 574-
co-ordination of movements.
_ by, 575:
in substance of organs, 575.
influence of on blood-vessels,
142, 577.
on heart’s action, 128.
on involuntary motion, 574.
on nutrition, 388, 575.
on secretion, 408, 575.
physiology | of, 570-78.
structure of, 567-70.
Synovial fluid, secretion of, 398.
membranes, 396.
Syntonin, 15.
Systemic circulation, 101. See
Circulation.
vessels, 103.

T.

Tact, 623. See Touch.
Tannic acid, test for gelatin, 12.

eer eee

INDEX. , 819

Tanno-gelatin, 7.
Taste, 697.
conditions for perception of, 697.
connection with smell, 705.
impaired by injury of facial
nerve, 551.
of fifth nerve, 547.
nerves on which the sense de-
pends, 555, 703, 704.
permanence of impressions, 705.
seat of, 698.
subjective sensations, 706.
variations of, 704.
Taurin, sulphur combined with,
325, note.
Taurocholic acid, 323.
Teeth, 50.
development and casting of, 54,

379-
parts of, 50.
structure of, 51.
temporary and permanent, 55.
Temperament, influence of blood,

4..
Temperature,
average of body, 231.
changes of, effects of, 234.
circumstances modifying, 232.
of cold-blooded and warm-
blooded animals, 235.
in diseases, 234. ‘
increased power of sapporting,
241.
influence on amount of carbonic
acid produced, 213.
on nerves; 476.
loss of, 238.
maintenance of, 236.
of Mammalia, birds, etc., 234.
modified by age, etc., 232.
of paralysed parts, 243.

oretteae of, 238
relation of to combustion of car-
bon and hydrogen, 236.
of respired air, 211.
sensation of variations of, 712.
See Heat.
Temporary cartilage, 41, 43.
teeth, 55.
Tendinous cords, 106.
Tendons, structure of, 37.
Tenor voice, 614.
Tensor tympani muscle, 674.
office of, 688.

Tesselated epithelium, 30.
Testicle, 731.
development of, 777.
structure of, 731.
Tetanus, reflex movements in, 507.
Thalami optici, function of, 521.
Third cerebral nerve, 539.
Thirst,
allayed by cutaneous absorption,
439.
cause of, 84.
sensation of, 291.
Thoracic duct, 349.
its contents, 361.
Thorax, 99.
Thymus gland, 411.
function of, 414.
Thyro-arytenoid muscles, 610,
Thyroid gland, 411, 413.
functoin of, 415.
Thyroid cartilage, structure and
connections of, 607, 608.
Timbre of voice, 61 5.
Tissue, adipose, 38.
areolar, cellular,or ponTedtive, 35.
fatty, 38.
muscular, 580.
Tissues,
absorption of, 365.
elementary, structure of, 29.
decay and removal of, 375.
erectile, 183.
mutually excretory, 95.
nitrogenous, urea derived from,

45
seats of. See Nutrition.
relation to blood, 167.
vascular and non-vascular, 385.
Tone of blood-vessels, 142.
of muscles, 508.
of voice, 615.
Tongue, 698.
action of in deglutition, 264.
in sucking, 225.
epithelium of, 702.
function of in speech, 622.
influence of facial nerve muscles
of, 552.
motor nerve of, 565.
an organ of touch, 703.
papille of, 698, 700.
parts most sensitive to taste, 55,

703.
structure of, 698.
3G 2

820

Tooth-ache, radiation of sensation |

in, 486
Tooth-fang, 50.
absorption of, 379.
Tooth-pulp, 51, 52, 55-
Touch, 706.
after-sensation of, 711.
characters of external bodies as-
certained by, 707.
conditions for perfection of, 708.

connection of with muscular

sense, 709.
co-operation of mind with, 711.
function of cuticle with regard
to, 426.
of papille of skin with regard
to, 424.
the hand an organ of, 708.
modification of, 708.
a modification of common sen-
sation, 623, 706.
special organs of;. 707.
subjective sensation of, 712.
the tongue an organ of, 704.
Touch-corpuscles, 423, 471.
Trachea, 99.
structure of, 188.
Tracts of medulla oblongata, 509.
of mucous membrane, 398.
of spinal cord, 490.
Tradescantia Virginica,
ments in cells of, 20.
Tragus, 671.
Transference of impressions, 485,

move-

499.
Transplanted skin, sensation in, 481.

Tricuspid valve, 105.
safety-valve action of, 115.
Trigeminal or fifth nerve, 543.
effects of injury of, 388, 546.
Trochlearis nerve, 541.
Trophic nerves, 388, 475.
Tube, Eustachian, 687.
Tubes, Fallopian. See Fallopian
tubes.
looped, of Henle, 442.
Tubular glands, 401.
convoluted, 403.
simple, 401.
of intestines, 310.
of stomach, 268.
Tubules, general structure of, 28.
Tubuli seminiferi, 742.
uriniferi, 441.

INDEX.

Tunica albugines of testicle, 731.
Tynpanum or middle ear, 673.
development of, 773.
functions of, 683.
membrane of, 673.
structure of, <b.
use of air in, 685.
Types of respiration, 198.

U.

Ulceration of parts attending in-
juries of cite 386, 547, 548.
Ulnar nerve,
effects of compression of, 479.
of division of, 482.
Umbilical arteries, contraction of,
139.
vesicle, 745.
Understanding, relation of to cere-
brum, 533-
Unstriped muscular fibre, 581.
Urachus, 749.
Urate of ammonia, 458.
of soda, 457, 458.
Urea, 452.
in blood, 83, 455.
chemical composition of, 453.
identical with cyanate of am-
monia, 453.
properties of, 453.
quantity of, 454.
in relation to muscular exertion,
455, 603.
sources of, 454.
Ureter, 441.
arrangement of, 447.
Urethra, development of, 782.
Uric acid, 456.
in blood, 33. '
condition in which it Mats in
urine, 457.
forms in which it is deposited,

457-
proportionate quantity of, 457.
source of, 457.
Urina sanguinis, pottis, et cibi, ©

449.

Urinary bladder, action of, 447.
development of, 779.
evacuation of, a reflex act, 505.
hypertrophy of, 392.
regurgitation from prevented, 447

*

INDEX. 821

Urine, 446-463.

analyses of, 451.
animal extractive in, 459.
chemical composition of, 450.
chlorine in, 462.
colour of, 448.
colouring matter of, 459.
creatin and creatinin in, 460.
cystin in, 462.
decomposition of by mucus, 459.
expulsion of, 448.
flow of into bladder, 447.
gases in, 463.
general properties of, 448.
hippuric acid in, 458.
mucus in, 459.
oxalic acid in, 462.
phorphorus in, 461.
quantity secreted, 450.
reaction of, 448.

made alkaline by diet, 449.
saline matters in, 460.
secretion of, 446.

effects of posture, etc., on,

447-

rate of, ib.
specific gravity of, 449.
sulphur in, 460
urea in, 452.
uric acid in, 456.
variations of, 449.

of water in, 452.

Uterus, 716.
changes of mucous membrane
Cn eee

contractions of its arteries, 139.
development of in pregnancy,

392.
follicular glands of, 753.
reflex action of, 506.
simple and compound glands of,

754-
structure of, 716.
Utriculus of labyrinth, 678.
Uvula in relation to voice, 618.

Vv.

Vagina, structure of, 717.

Vaginal veins of liver, 318.

Vagusnerve. See Pneumogastric.

Valve, ileo-ceecal structure of, 311.
of Viessens, 531.

Valves of heart, 104.
action of, 112-19.
bicuspid or mitral, 105.
semilunar, 108
tricuspid, 105.
of lymphatic vessels, 353.
of veins, 168
Valvule conniventes, 298.
Vas deferens, 731.
Vasa efferentia, 445, 732.
recta, 445, 732. °
vasorum, 134.
Vascular area, 750.
Vascular glands, 410.
analogous to secreting glands,
410.
in relation to blood, 414.
several offices of, 415-18.
Vascular parts, nutrition of, 385.
system, development of, 763.
Vaso-motor nerves, 142, 575.
Vaso-motor nerve-centre, 576.
reflection by, 577.
Vascularity, degrees of, 159.
Vegetable matters, absorption of,

437-
Veen substances, digestion of,
204.
Vegetables and animals, distinc-
tions between, 4.
Veins, 100, 167.
absorption by, 367.
anastomoses of, 171.
circulation in, 169.
coats of, 167.
of cranium, 181.
effects of muscular pressure on,
170.
of respiration on, 174.
in erectile tissues, 183.
force of heart’s action remain-
ing in, 170.
influence of gravitation in, 169.
muscular tissue in, 172.
rythmical action in, 7.
structure of, 167.
systemic, 103.
valves of, 168.
velocity of blood in, 175.
Velocity of blood in arteries, 175.
in capillaries, 162.
in veins, 175.
of circulation, 176.
of nervous force, 478.

822

Vena porte, its arrangement, IOI,

17.
vetige blood, characters of, 85-9.
Ventilation, necessity of, 214.
Ventricle, fourth, of brain, 511,531.
Ventricles of heart, 102.
capacity of, 128.
contraction of, IIo.
effect on arteries, 144,149.
on circulation, 132.
on veins, 170,
force of, 126.
development of, 766.
dilatation of, 112.
of larynx, office of, 619.
Ventriloquism, 694.
mechanism of, 7d.
Vermicular movement of intes-
tines, 345.
Vermiform process, 524.
Vertebre, development of, 744,759.
Vesicle, germinal, 720.
Graafian, 715, 718.
bursting of, 723-25.
umbilical, 745.
Vesicles of vascular glands, 411.
Vesicula, germinativa, 720.
. Vesicule seminales, 735.
functions of, 736.
reflex movements of, 505.
Vesicular nervous substance, 473.
Vestibule of the ear, 676.
of vagina, 717.
Vibrations, conveyance of, to au-
ditory nerve, 683.
perception of, 627.
of vocal cords, 617.
Vidian nerve, 550.
Villi of intestines, 306.
action in digestion, 338.
on intestinal glands, 301.
Villi of chorion, 751.
in placenta, 756.
Visceral arches, development of,
761.
ee serous membranes of,
396.
lamine, 745, 761.
layer of pleura, 188, note,
Vision, 636,
angle of, -655.
at different distances, adapta-
tion of eye to, 649-51.
contrasted with touch, 656.

INDEX.

Vision, continued.
corpora Rs adrigemina the prin-
cipal nerve-centres of, 521.
correction of aberration, 648,
649. ’
of inversion, 653.
direction of, 656.
direction of: rays in, how regu-
lated, 642.
distinctness of, how secured, 646.
double, 666.
duration of sensation in, 650.
estimation of the form of ob-
jects, 656.
of their motion, 657.
of their size, 654.
field of, size of, 7b.
focal distance of, 649.
impaired by lesion of fifth
nerve, 546, 547.
influence of attention on, 658.
modified by different parts of
the retina, €62.
organ of, 636. See Eye.
phenomena of, 644.
in quadrupeds, 667.
single, with two eyes, 664.
its cause, 667-71.
structures essential for, 645.
Visual direction, 656.
Vital capacity of chest, 202.
motions, 578. ;
Vitality. See Life.
Vitelline duct, 745.
membrane, 719, 740.
spheres, 740.
Vitellus, or yelk, 720. See Yelk.
Vitreous humour, 644.
Vocal cords,
action of in respiration, 200, 222.
approximation of, effect on
height of note, 612.
attachment of, 608.
elastic tissue in, 37.
longer in males than i in females,

615.
position of, how modified, 610.
vibrations of, cause voice, 604,

ook itions on which strength
depends, 618,

INDEX. 82 3

Voice, human, produced by vibra-
tion of vocal cords, 604, 618.
impaired by destruction of acces-
sory nerve, 564.
in eunuchs, 616.
influence of age on, 615.
of rk of palate and uvula,
618.
of epiglottis, 612.
of sex, 614.
‘influence of ventricles of larynx,

19.
of vocal cords, 604, 610.
in male and female, 614.
cause of different pitch, 615.
modulations of, 617.
natural and falsetto, 2.
peculiar characters of, 616.
varieties of, 614.

Volatile bodies, influence of, on
sense of smell, 633.
Voluntary muscles. See Muscles.

Vomiting,
action of stomach in, 289.
mechanism of, 223.
influence of spinal cord in, 505.
voluntary and acquired, 290.
Vowels and consonants, 619.
Vulvo-vaginal glands, 718.

W.

Walking, muscular action in, 598,
601.
Warm-blooded animals, 235.
Water,
absorbed. by skin, 437.
by stomach, 281. _
in blood, variations 1n, 79.
conduction of sound through, 683
deficient in thirst, 84.
exhaled from lungs, 217, 435.
from skin, 433-

Water, continued.
forms large part of human body,
I

influence of on coagulation of
blood, 66, 67.
_ on decomposition, 10.
in urine, excretion of, 446.
variations in, 452.
vapour of in atmosphere, 210.

Wave of blood in the pulse, 149.

Weight, relation to capacity of
chest, 202.

sensation of, 710.

White corpuscles. See Blood-cor-
puscles, white ; and Lymph-
corpuscles.

fibro-cartilage, 41, 43.

White substance of nerve-fibre,
466

Will,

reflex actions amenable to, 503-
5, transmission of through cord,

498.
Willis, circle of, 181.
Wolffian bodies, 777.

<x

Yelk, or vitellus, 720.
changes of, in Fallopian tube,

in uterus, 742.
cleaving of, 740
constriction of by ventral
lamina, 745.
Yelk-sac, 747.
Yellow elastic fibre, 37.
fibro-cartilage, 41, 43.
spot of Sémmering, 639, 641.

Z.
Zona pellucida, 719, 740.

a

PAGE

9

LIST OF WORKS REFERRED TO.

——4———

- SMEE. Proc. R. Soc. 1863.
. PREPONDERANCE OF MAGNESIA OVER LIME IN JUICE OF MUSCLES.

Liebig. Chemistry of Food. 1847.

. 7th line from t. BrerNanp. Legons de Phys. Expérimentale.

Paris, 1859.

Savory. On the relative Temperature of Arterial and. Venous
Blood. Pamphlet.

13th line Srom b. BrErnarp. The Medical Times and Gazette.
April 21, 1860.

BarrveL. Annales d’Hygitne Publique et de Médecine Légale.

. VALENTIN. Repert. f. Anat. und. Phys. Bd. iii., p. 281.

Buake. Prof. Dunglison: Physiol. 7th Ed., vol. ii, p. 102.

LreHMANN. Physiolog. Chem. Cavend. Soc. Edit., vol. ii, p.
269. )

BERNARD. Legons. 1859. T. i. p. 419.

. ALEXANDER ScumiptT. Archiv. fiir Anatomie, Physiologie, etc.

By Reichert and Du Bois-Raymond, being a continuation of
Neil’s, Meckel’s, and Joh. Miller’s Archiv. Leipzig, 1861,
p- 545; and 1862, pp. 428 and 583.

ANDREW BucHANAN. Proceedings of the Glasgow Philosophical
Society. Feb., 1845. —

. GULLIVER. London Medical Gazette. Vol. xli., p. 1087,

Wuarron Jones. Philosophical Transactions. 1846.

. Lernmann. Dr. Geo. E. Day : Chemistry, in relation to Physio-

logy and Medicine, p. 216. 1860, Bailliére.
ENDERLIN. Annalen der Chemie und Pharmacie. Von Liebig
und Wohler. 1844.

. Denis. F. Simon: Animal Chemistry. Translated by Dr. Day

for the Sydenham Soc.

. JoHN Davy. Anat. and Phys. Researches. Vol. ii., p. 28.

Pottr. Researches and Experiments upon the Human Blood.
Noticed in the Medico-Chirurgical Review, Oct., 1847.

. Pror. Stokes. Proceedings of the Royal Society. 1863-4.
. Harvey’s Works. Syd. Soc. Edition. 1847, p. 31.

826

PAGE

118,

LIST OF AUTHORS.

W. S. Savory. Observations on the Structure and Connection
of the Valves of the Human Heart. Pamphlet, 1851.

. VALENTIN. De Functionibus Nervorum Cerebralium et Nervi

Sympathetici. Berne, 1839. Bd. i., p. 427.

. Dr. Reip. The Cyclopedia of Anatomy and Physiology. Edited

by Dr. Todd. Vol. ii., p. 606.

. Kiirscuner, R. Wagner: Handwéorterbuch. der Physiologie.

Braunschweig. Art. Herzthitigkeit.

. Margy. Physiologie Médicale de la Circulation du Sang. 1863.
. Dr. Guy. Guy's Hospital Reports. -Nos. vi. and vii.
. VALENTIN. Lehrbuch der Physiologie des Menschen. Bd.i,

p- 415, etc. Braunschweig, 1844.

. OESTERREICHER. Lehre vom Kreislauf des Blutes. p. 33.

Niiremberg, 1826.

. GANGLIA IN THE SUBSTANCE OF THE HEART. Remak. Medi-

cinische Zeitung des Vereins fir Heilkunde in Preussen.
No. ii. 1840.

VoLKMANN. Miiller: Archiv. fiir Anatomie, Physiologie, und
wissenschaftliche Medicin. 1844, p. 424. Berlin.

Dr R. Lee. Proceedings of the Royal Society. 1847.

London Medical Gazette. Vol. xlv., p. 224.

Pacer. Reports on the Use of the Microscope, and On the Pro-
gress of Human Anatomy and Physiology, in the British and
Foreign Medical Review. 1844-5, p. 13.

. PAGET. Proceedings of the Royal Society. May, 1857.
. SHArPey. Edinburgh Medical and Surgical Journal. Vol.

lxiii., p. IO.

. JOHN Hunter. Works of, Edited by Mr. Palmer. Vol. iii.,

p- 157. London, Longmans, 1835.

. E. H. Weser. Miller: Archiv. fiir Anatomie, Physiologie, und

wissenschaftliche Medicin, 1847, p. 232. Berlin.
Pror. Kétuiker. British and Foreign Medico-Chirurgical Re-
view. July, 1850, p. 241.

. W. 8. Savory. On the Shape of Transverse Wounds of Blood-

vessels. Pamphlet, 1859.

. THomas Youne. Philosophical Transactions. Vol. xcix.

PoOISEUILLE. Magendie: Journ. de Phys. T. viii., p.'272.

. 10thline from t. PoIsEUILLE. Comptes Rendus des Séances de

l’Académie Royale des Sciences de Paris, 1860, p. 238.

. Lupwie. Miiller: Archiv., etc. 1847, p. 242.
. For instances of occasional direct communications between arterics

and veins see Suchet: Bulletin de ?Acad. de Méd. T. xxvi.
p. 825.

LIST OF AUTHORS. 827

. MarsHatn Hatt. Edinburgh Med. and Surg. Journ. 1843.
- HAtEs. Statist. Essays. Vol. ii. London, 1740.

Weser. Miiller: Archiv. fiir Anat. Phys., und wissenschaftliche
Medicin. Berlin, 1838, p. 450.

VALENTIN. Lehrbuch der Phys. des Menschen. Braunschweig,
1844, Vol. i. p. 468.

. Burpon SANDERSON. Holmes’s System of Surgery. Vol. v.

Art. Inflammation. 1871.
Water. Philosophical Magazine. Vol. xxix., 1846.

. Mocx. Henle and Pfeufer: Zeitschrift fiir Rationelle Medizin.

Heidelberg, 1845, p. 33.
VALENTIN. Lehrbuch der Phys. des Menschen. Braunschweig,
1844, P. 477:

. WHARTON JONES. Philosoph. Trans. 1852.
. Lupwic. Miiller: Archiv. fiir Anat. Phys., und wissenschaft-

liche Medicin. Berlin, 1847, p. 242.

. VALENTIN. Lehrbuch der Phys. des Menschen. Braunschweig,

1844, p. 478.

Lupwic. Miller: Archiv. fiir Anat., Phys., und wissenschaft-
liche Medicin. Berlin, 1847, p. 242.

Burpon SANDERSON. Proc. of the Royal Soc. 1867.

. PoIsEvILLE. Annales des Sciences Naturelles: Zoologie. 1843.
. J. Buaxe. Edinburgh Medical and Surgical Journal. Oct.»

1841.

. Ketire. London Med. Gaz. May, 1843.

Burrows. Disorders of the Cerebral Circulation. 1846.

. GuenTHER. Meckel: Archiv. fiir Anat. und Phys. 1828,

p- 364.

. Kéuurcer. Das anatomische und physiologische Verhalten der

cavernisen ,Kérper der Sexualorgane.
Koxzexrt. Spallanzani: Versuch iiber das Verdauungsgeschiift.
- Leipzig, 1785.
Le Gros Crark. London Med. Gaz. Vol. xviii., p. 437.
Krause. Miiller: Archiv. fiir Anat., Phys., und wissenschaft-
liche Medicin. Berlin, 1837.

. MM. Brav & Marssiat. Archives Générales de Médecine. 1842-3.

note, Hurcnrnson. ‘Trans. of the Royal Med.-Chir. Soe.
Vol, xxix.

. Bourcrery. Archives Générales de Médecine. 1843.

E, Smith. Carpenter: Princ. of Human Phys. Edited by

H. Power. 1864.
Hvurconrson. Trans. of the Royal Med.-Chir. Soc. Vol,

XX1X,

828

LIST OF AUTHORS.

‘ ; ep. of Med.-Chir. Committee. Trans. of the Royal Med.-Chir.

Soc. 1862,

. RADCLYFFE Hatt. On the Action of the Muscular Coat of the

Bronchial Tubes.. Pamphlet, 1851.
GAIRDNER. Monthly Journ. of Med. Science. Edinburgh.
' May, 1851.

. C. J. B. WiutrAMs. Carpenter: Princ. of Human Phys.: 3rd ed.,

p. 588.
VoLKMANN. R. Wagner: Handworterbuch der Phys. Braun-
schweig. Art. Nervenphysiologie, p. 586.

. VALENTIN & BrunNER. Lehrbuch der Phys. des Menschen.

Braunschweig, 1844. Vol. i., p. 547.
Ep. Smiru. Philosoph. Trans. 1859.
ANDRAL ET GAVARRET. Recherches sur la quantité d’ Acide Car-

bonique exhalé par le Poumon. Paris, 1843.

. ViERoRDT. Phys. des Athmens. 1845.
. LETTELLIER. -Annales de Chemie et de Physique. . 1845.

Ep. Smiru. Philosoph. Trans. 1859.
ALLEN & Pepys. Philosoph. Trans. 1808-9.

. Lrnmann. Dr. Geo. Day : Chemistry in Relation to Phys. and

Med. 1860. Bailliére. p. 469.

Ep. Smiru. Philosoph. Trans. 1859.

. VALENTIN & Brunner. Lehrbuch der Phys. des Menschen.
Braunschweig, 1844. Bd. i.

. BEeNcE JoNES. Chem. Gaz. April, 1851.

Brenck Jones. The Med. Times. August 3oth, 1851.

Reenavtt & Reiser. Brit. and For. Med.-Chir. Rev. July, .
1850, p. 252.

Liesic. Animal Chem. Trans. by Dr. Gregory. 3rd Ed.
p- 184.

. Ransome. Cambr. Jour. of Anat. and Phys., May, 1870.
. Eccies. London Med. Gaz. Vol. xliv., p. 657.
. Report of Med.-Chir. Committee. Trans. of the Royal Med.-Chirur.

Soc. 1862.

. Marsuart Hart. The Cyclopedia of Anat. and Phys. Ed.

by Dr. Todd. Vol. ii, p. 771.

- WUNDERLICH. Med. Thermometry. Transl. by B. Woodman,

M.D. New Syd. Soc. Trans. 1871.

- OcLe. St. George’s Hosp. Reports. Vol. i.

GrEE. Gulstonian Lectures. Brit. Med. Jour. 1871. -

Davy. Proceedings of the Royal Soc., June, 1845.

TIEDEMANN AND Rupoirui. Tiedemann: Phys. translated by
Gully and Lane, p. 234.

LIST OF AUTHORS. 829

. JOHN Hunter. Works of, Ed. by Mr. Palmer. 1835. Vol. iii.,

p. 16, and vol. iv., p. 131, cé seq.

. Newport. Philosoph. Trans. 1837.
. C. JAMES. Gazette Médicale de Paris, April, 1844.
. Earnie. Trans. of the Royal Med.-Chir. Soe. Vol. vii., p.

£73:

. CHossaT. Gaz. Méd. de Paris, Oct. 1843.

LETTELLIER. Annales de Chimie et de Physique. 1844.

. Wricut. The Lancet. 1842-3.
. OwEN. Dr. Carpenter: Princ. of Human Phys. 5th ed., 1855,

p- 76, note.

. Bernarp. The Med. Times and Gaz. July 7th, 1860.
. BRINTON. On Food and its Digestion, Churchill, 1861.
. Beaumont. Experiments and Observations on the Gastric Juice,

and the Phys. of Digestion, by W. Beaumout. U. S. 1834.
Reprinted, with notes, by Dr. A. Combe. Edinburgh, 1838.

. Bronpuor. Traité Analytique de Digestion. 8vo, Paris, 1844.

BERNARD. Gaz. Méd. de Paris. June, 1844.

Chem. in relation to Phys. and Md., by Dr. G. E. Day. 186c.
Baillitre. p. 158.

Gro. E. Day. Chem., etc., p. 159.

. Beaumont. Experiments aiid Observations on the Gastric Juice,

and the Phys. of Digestion, by W. Beaumont. U.S., 1834.
Reprinted, with notes, by Dr. A. Combe. Edinburgh, ‘1838,
p- 120.

. Gossr. Spallanzani: Versuch tiber das Verdauungsgeschift.

Leipzig, 1785.

_ Rawirz. Weber: die Einfachen Nahrungsmittel. Breslau,

1846.

. Bernard. Gaz. Méd. de Paris. 1850, p. 889.
. Brinton. London Med. Gaz., 1849.

Brixton. On Food and its Digestion. Churchill, 1861,
p. 100.

. Bernarp. The Med. Times and Gaz. Aug., 1860.

Loneer. Anat. et Phys..du Syst?me Nerveux, etc. Paris, 1842.
Vol. i., p. 323.

Biscnorr. Miiller: Archiv. fiir Anat. Phys. und wissenschaft-
liche Medicin. Berlin, 1848. Jahresbericht, p. 140.

- Meissner. Henle and Pfeufer: Zeitschrift fiir Rationelle Medi-

zin, Heidelberg, 2nd Ser., vol. viii. _

. LieperKtun, J. N. Diss. de Fabricd et Actione Villorum Intes-

tinorum tenuium. 1782.
Preyer. De Glanduris Intestinorum. 1682.

>?

LIST OF AUTHORS.

. Bruny, J. C. Glandule Duodeni seu Pancreas secundarium.

‘

4to. 1715.

. MM. Bovcwarpat & SANDRAS. Gaz. Méd. de Paris. Jan.

1845.
DISCHARGE OF Fatty MATTERS FROM INTESTINE. ‘Trans. of the

Royal Med.-Chir. Soc. Vol. xviii., p. 57.

. BERNARD. Quarterly Jour. of Microscop. Science. Churchill.
. TABULAR COMPOSITION OF BILE, by Frerichs. V. Gorup-Besanez.

Physiologie Chemie. 1862, p. 469.
PRESENCE OF Copper IN BILE AND BrutAry Cancun. Gorup-
Besanez. Untersuchungen tiber Galli. Erlangen, 1846.

. Buonpior. Essai sur les Fonctions du Foie. Paris, 1846.

p. 62. .

Kemp. Chemical Gaz. No. 99, 1846.

Smon. . Animal Chem. Trans. by Dr. Day for the Sydenham
Soc. Vol. ii., p. 367.

Frericus. Ranking: Half-yearly Abst. of the Med. Sciences.
Churchill, Vol. iii., 314.

Pavy. Phil. Trans. 1860, p. 595.
Pavy. On the Nature and Treatment of Diabetes. Churchill.
1862.

Brinton. On Food and its Digestion. Churchill. 1861.

K6LLIKER. Annales des Sciences Naturelles. Geologie. 1846,
p- 99.

RECKLINGHAUSEN. Art. Lymphatic System. Stricker’s His-
tology, translated by H. Power. Vol. i.

. Korirker. Brit. and For. Med.-Chir. Rey. July, 1850.
. GULLIVER. Hewson : Works, Ed. for the Syd. Soc. by Mr. Gulli-

ver, 1846—7, p. 82, note.

. Ascnerson. Miiller: Archiv. fiir Anat. Phys. und wissenschaft-

‘liche Medicin. Berlin, 1840.

. Bovisson. Gaz. Méd. de Paris. 1844.
. OwEN ReEs. London Med. Gaz. Jan., 1841.

R. Vircoow. Die Cellular Pathologie (since translated by Dr.
Chance). Berlin, 1858, s. 143.

. Brpper. Miiller: Archiv. fiir Anat. Phys. und wissenschaftliche

Medicin. Berlin, 1845.

. Scumipt. New Syd. Soc.’s Year-book of Med., ete. London,

1863, p. 24.

. Herzst. Das Lymphagefiiss system und seine Verrichtungen.

Gottingen, 1844.
Lympu-Hearts, J. Miiller. Elements of Phys. transl. by Dr.
Baly. 2nd ed., 1840, p. 293.

395+

407.

LIST OF AUTHORS. 831

. VOLKMANN. Miiller: Archiv. fiir Anat. Phys. und wissenschaft-

liche Medicin. Berlin, 1844.

. Bence JONES. Proceedings of the Royal Soc. Vol. xiv.
. SAvory. The Lancet. 1863, May 9 & 16.
. OESTERLEN. Oesterreichische Medecinische Wochenschrift. Wien,

Feb., 1844.
OESTERLEN. Archiv. fiir Phys. und Pathol. Chemie und Mikro-
scopie. VonJ. F. Heller. Wien, 1847, p. 56.

. Hetmnourz. Miller: Archiv. fiir Anat. Phys. und wissenschaft-

liche Medicin. Berlin, 1845.

. CARPENTER. Princ. of Human Phys. 3rd ed., p. 623.
. Bropiz. Lectures on Pathol. and Surg. 1846, p. 309. —
Travers. Further Inquiry concerning Constitutional Irritation.

p- 436.

. Baty. J. Miiller: Elements of Phys. Transl. by Dr. Baly. 2nd

ed., 1840, p. 396.
Defective Nutrition from Irritation of Nerves: London Med. Gaz.,
Vol. xxxix., p. 1022.
Bowman. The Cyclopedia of Anat. and Phys., Edited by Dr.
Todd. Art. Mucous Membrane.
PERISTALTIC MoveMENTS oF LARGE GLAND-DucTs. J. Miiller :

Elements of Phys. Translated by Dr. Baly. 2nd ed., 1840,
p. 521.
Dr. Brown-Sfquarp. Journ. de Phys. 1858.

. CARPENTER. Prine. of Human Phys. 3rd ed., p. 476.

Srmon. <A Physiological Essay on the Thymus Gland: London,
1845. 4to.

. Ecker. Der feinere Bau der Neben-nieren beim*Menschen und

den Vier Wirbelthierclassen. Braunschweig, 1846.

. Meyer. Boehm, L. De Glandularum intestinalium Structura

penitiori. Berol., 1835. March, 1845.

. Srwon. A Physiological Essay on the Thymus Gland. London,

1845. 4to.

FRIEDLEBEN. Die Phys. der Thymusdriise. Frankfurt,
, 1858.

Hurcurson. Funke: Atlas der Phys. Chemie. Leipzig,
1863—6.

Witxes. Guy’s Hosp. Rep. 1862.

Koétirker. Manual of Human Microscop. Anat. Parker, 1860,

p- 374- cash

. Kotirxer. Manual, ete. p. 365.
. Krause. R. Wagner: Handwiérterbuch der Phys. Braunschweig.

Article Haut.

LIST OF AUTHORS.

.

Erasmus Wiison. A Practical Treatise on Healthy Skin.
Churchill, 1846. .

. J. DAvy. Trans. of the Royal Med.-Chir. Soc. Vol. xxvii., p, 189.

KRAvsE. Bulletin de l’Académie Royale de Médecine.

BerzeEuivs. Traité de Chimie, traduit par Esslinger. 8 vols.
8vo. Paris. Vol. vii. contains the Chemistry of Animal
Structures.

ANSELMINO. Zoochemie, by D. Lehmann. Heidelberg, 1858, p. 301.

Gorup-BrsaNnrEz. Lehrbuch der Phys. Chemie. 1862, p. 504.

LAVOISIER & Sequin. Mémoires de l’Acad. des Sciences de Paris.
1790.

. Krause. Paget: Reports on the use of the Microscope, and on

the Progress of Human Anat. and Phys. ; in the Brit. and
For. Med. Rev. 1843-4, p. 40.

. Mitne-Epwarps. Influence des Agens Physiques sur la Vie.

Trans. by Dr. Hodgkin. |
ReGNAULT & Retset. Annales de Chimie et de Pharmacie. 1849.
EpwaArp Smiru. Dr. Carpenter: Princ. of Human Phys. 5th

ed., 1855. O6thed., p. 293.

MrtnE-Epwarps & Mi.ier. J. Miiller: Elements of Phys. ;

Trans. by Dr. Baly. 2nd ed., 1840, p. 328.

. Macrenpig. Gaz. Méd. de Paris. Dec., 1843.
. Miznz-Epwarps. Influence des Agens Physiques sur la Vie.

Translated by Dr. Hodgkin. ;
MappEN. Experimental Inquiry into the Phys. of Cutaneous
Absorption. Edinburgh, 1835.
BertHotp. Miller: Archiv. fiir Anat., Phys., und wissen-
schaftliche Medicin. Berlin, 1838, p. 177.

. Ertcusen. London Med. Gaz. 1845.
. BERNARD. Comptes Rendus des Séances de l’Académie Royale

des Sciences de Paris. 1846.

. Prout. On the Nature, etc.
. GoLpInc Brrp. Urinary Deposits. 1844, p. 31.

Parkes. On the Composition of the Urine. 1866.

. Wouter. Annales de Chimie et de Pharmacie. xxvii., 196.
. Lecanu. Bulletin de Acad. Royale de Méd. T. xxv., p, 261.
. LeHMANN. F. Simon: Animal Chem. Trans. by Dr. Davy for

the Syd. Soc. Vol. il., p. 163.
LASsIGNE. Journal de Chimie Médicale. p. 272.

. Mitton. Comptes Rendus des Séances de l’Acad. Royale des

Sciences de Paris. 1843.
G. Brrp.. London Med. Gaz. Vol. xli., p. 1106,

. Lizsic. The Lancet. June, 1844.

LIST OF AUTHORS, 833

PAGE

458. Lresic. The Lancet. June, 1844.

>» WEISMANN. Henle and Pfeufer: Zeitschrift fiir Rationelle
Medizin. Heidelberg. 3 ser., p. 337. |

»» Ure. Transac. of the Royal Med.-Chir. Soc. Vol. xxiv.

459. Lizsie. Chem. of Food. Walton and Maberly, 1847.

», Hentz. Canstatt: Jahresbericht tiber die Fortschritte in der
Biologie. Erlangen, 1847, p. 105.

461. Ronaups. Philosophical Mag. 1846.

467. Lister & TurNER. Quar. Jour. of Microscop. Science. 1859.

», Lockwarr CiarKE. Philosoph. Transac. 1859.

», Stine. Ueber den Bau der Nerven-primitivfaser und der
Nerven-zelle. 1856. |

470. Gutu. The Med. Times. 1840.

471. Ko.urker. Manual of Human Microscopic Anat. Parker, 1860,
p. 248.

»» Pacrni. Annali Universali di Medicini. Luglio. 1845, p. 208.

478. Hetmnoitz & Baxt. Camb. Journ. of Anat. and Phys. P. i,
new series, p. 190.

»» RuTHERFORD. Lancet, April rst, 1871.

482. Savory. The Lancet, August Ist, 1368.

492. LockHART CLARKE. Philosoph. Transac. 1851 to 1859.

494. KéniiKer. Manual of Human Microscopic Anat. Parker. 1860,

. 244. ,
497. Pn arp On the Phys. and Pathol. of the Cerebral
Nervous System. Philadelphia, 1860,
508, VotkMANN. Miiller: Archiv fiir Anat. Phys. und wissen-
schattliche Medicin. Berlin, 1844. .
517. J. Rerp. Edinburgh Med. and Surg. Journ, 1838.
526. Loncrer. Anat. et Phys. du Systéme Nerveux, ete. Paris, 1842.
T. i, p. 733, and others. .
527. Fuourens. Recherches Expérimentales sur les Fone. du Systeme
- Nerveux, etc. Paris.
,, Macenvre. Legons sur les Fenctions du Systéme Nerveux.
,, Bovrrzaup. Recherches Cliniques et Expérimentales sur le
Cervelet. Referred to by.
Loncet. Anat. et Phys. du Systéme Nerveux, etc. Paris, 1842.
T. i, p. 740.
529. Lonert. Anat. et Phys. du Systéme Nerveux, etc. Paris, 1842.
T..i5: pe 762.
ComBIETTE. Revue Médicale.
541. GRANT. See Longet, 1, ¢. T. ii., p. 388.
546. VALENTIN. Lehrbuch der Phys. des Menschen, Braunsehweig,
1844. Vol. ii, p. 666.
‘ 3H

834 LIST OF AUTHORS.

554. Rerp. Edinburgh Med. and Surg. Journ. 1838.
558. Bripper & VoLKMANN. R. Wagner: Handworterbuch der Phys,
Braunschweig. Art, Nervenphysiologie.
559. Rump. Edinburgh Med. and Surg. Journ. Vols. xlix. and li.
561. Rew, Edinburgh Med, and Surg. Journ. Vols. xlix. and li.
,, Lecatiors, Céuvres Completes, Edited by M. Poriset. Paris,
1830. ;
>, TRAUBE. ‘Beitriige zur Experimentellen Pathologie und Phys.
' Berlin, 1846.
565. Bernarp. Archives Générales de Médecine. 1844.
579. Kiune. Camb. Journ. of Anat. and Phys. Part ii.
581. K6LLIkER. Manual of Human Microscopic Anat. Parker, 1860,
p. 63. .
586. SHARPEY. Quain: Anat. 7th ed.
», SEGALAS. J. Miiller: Elements of Phys, Trans. by Dr. Baly.
2nd ed., 1840, p. 895.
588. Bowman. Phil. Trans., 1840, 1841.
589. No DimrnvTion In BuLK oF Conrractina MusciE. Mayo,
J. Miller: Elements of Phys. ; Trans. by Dr. Baly. 2nd ed. ©
1840, p. 886. Valentin ; Lehrbuch der Phys. des Menschen.
Braunschweig, 1844. Matteucci: Erdmann’s Jour.
» Ep. Weser. R. Wagner: Handworterbuch der Phys. Braun-
schweig. Art. Muskelbewegung.
591. Ep. WEBER, R. Wagner: Handworterbuch der Phys. Braun-
schweig. Art. Muskelbewegung.
593. ScuirFER: Camb. Journ, Part ii., new series, p. 416; Part iii.
new series, p. 236.
,, Brown-S&quarp. Proc. of the Royal Soc. 1862, p. 204.
», Brown-Séquarp. London Med. Gaz. May 16, 1851.
594. VALENTIN. Lehrbuch der Phys. des Menschen. Braunschweig,
1844. Bd. ii, p. 36.
617. PETREQUIN & Dipay. Gaz. Méd.. de Paris.
622. MULier & CotompBart. Froriep : Neue Notizen aus dem Gebiete
| der Natur. Weimar, 1840. |
625. MacEnpre. Journ. de Phys. T. iv., p. 180.
653. VOLKMANN. R. Wagner: Handwéorterbuch der Phys, Braun-
schweig. Art. Sehen, p. 286. .
686 note. Ep. Wrser. Archives d’Anat. Générale et de Phys.
1846.
707. ScuirF & Brown-SkQuaRD. The Lancet. 1858.
», SIEVEKING. Brit. and For. Med.-Chir. Rey. 1858, Vol. ii., p. 501.
709. VALENTIN. Lehrbuch der Phys. des Menschen. Braunschweig,
1844. Vol. ii, p. 566.

LIST OF AUTHORS. 835

AGE
722. VALENTIN. Miiller: Archiv fiir Anat. Phys. und wissenschaft-

liche Medicin. Berlin, 1838.
730. Daron. Phys. 1864, p. 585.
739. Biscnorr. Entwickelungs-Geschichte der Saugethiere und des
; Menschen. 1842. |
753. H. Miuier. Brit. and For. Med.-Chir. Rev. Vol. xiii., p. 546.
756. Harvey. On a remarkable Effect of Cross-Breeding. By Dr.
Alex. Harvey. Blackwood and Sons, 1851. ~
Hurcntnson. Med. Times and Gaz. Dec., 1856.
Savory. On Effects upon the Mother of Poisoning the Feetus.
Pamphlet, 1858.
765. K6LLIKER. Annales des Sciences Naturelles: Zoologie. Aug.,
1846.

99

9?

THE END.

BRADBURY, AGNEW, & CO., PRINTERS, WHITEFRIARS.

i. aS pe
ye rT
V\} Gea
i Okan
pallichinwn 4 Maren

fay
Ohl;

& ko L. Puce, dp . lowes
~ tabul = ¢obsafe

M Ph
ps

EFESF

‘
)
a
ad
~
<

|

University of Toronto

Library

DO NOT
REMOVE
THE
CARD
FROM
THIS
POCKET

Acme Lihrary Card Pocket
Under Pat. **Ref. Index File”
Made by LIBRARY BUREAU

rey ie J oe ~~ ~ _ —s

ebizass

tte

3

faa

. \) une

att

rly

3 <1

9

! M “ ese? .
A ; a : is t rattle
i seid } ‘i

Sa eneae

ve by ee

{ i

f

is

ui

¢
J
z

i)

Tate

ae